C#, 2760 bytes
namespace System{class P{static void Main(){var c="us>g System;us>g System.Draw>g;class p{publ' stZ' void c(){var b=(Bitmap)Bitmap.FromFile(Console.ReadL>e());Console.Write(!1,1[3,3#2?!4,4#1?!5,5#2?!@#1?!+$SupK UsK*Salesforce%]^$< F't~_Fantasy%8,8#6?$Arqade*Ask Ubuntu%@#6?$WordPress Development%8,8#4?!9,9#2?$Phys's*UsK ExpKience%+$Travel*Craft CMS%5,5^!@#6?!]#1?$TeX - LaTeX%+$Mi Yodeya*Meta Stack Exchange%]#6?$ProgrammK|2,2#5?$Christianity*MZhemZ'a%@[]^$MZhemZ'|0,0#1?$Cross ValidZed*Theoret'al ComputK <%2,2^!]#5?$Seasoned Adv'e*Drupal AnswK|]^$Graph' Design*WebmastK|2,2^!4,4#5?!5,5#2?!@^$Ask PZents*Home Improvement%@#6?$Android Enthusiasts*Skept'|5,5#4?!@#5?$Web Appl'Z~s*English/_Usage%@#4?!]#8?$SharePo>t*B'ycle|]#1?$Electr'al Eng>eK>g*DZabase Adm>istrZor|4,4^!5,5#2?!+$Game Development*Photography%@:SKvK Fault%+$Geograph' InformZ~ Systems*Unix_L>ux%5,5^!0`Stack Apps*The Workplace%+!@[]#4?$InformZ~ Security*Ask DiffKent%]:Role-play>g Games*PKsonal F>ance_Money%3,9#8?$Academia%5,15^$& > Japanese%0,13:&*& > Portuguese%2,2:MZhOvKflow%3,3:AviZ~%4,4^$LEGO AnswK|5,5[@[][0,1:PokK*Anime_Manga%+$BlendK*H>duism%][8,8:WritK|0,1^!2`RaspbKry Pi*W>dows Phone%+$Biology*Worldbuild>g%9,9:Movies_TV%8,8[6`Trid~*Islam%0,1:Mus', Pract'e_Theory*L>guist'|][@[9,9:Ches|+!4,6:Garden>g_Landscap>g*Susta>able Liv>g%4,6:Buddhism*Startup|8,8:English/ LearnK|3,4[6,7:Network Eng>eK>g%9,5:Magento%+$Motor Veh'le Ma>tenance_Repair*MZhemZ's EducZor|4,8:GKman/%7`Joomla%7,6[+$QuantitZive F>ance*Ardu>o%9`Chemistry*Cryptography%8,8[0,1^!@[3`Tor%4,5:French/*The GreZ Outdoor|3`Project Management%3,6:Ch>ese/*Space ExplorZ~%+!2,6:Programm>g Puzzles_Code Golf%@:Cognitive <s*Signal Process>g%1,0:Ebook|@[4,5:Earth <*BeK%8,5:Emacs*ExpZriZe|1`History of < and MZh%3,4[@[+$Homebrew>g%3,6:DZa <*Video Product~%5,7:Russian/%9,4[4,8:Bibl'al HKmeneut's*Philosophy%11,6:Board_Card Games*Bitco>%3,5[@[3,8:AmZeur Radio%5,6:Genealogy_Family History%6,9:Software Quality Assurance_Test>g*Open DZa%3,6[11,7:Code Review%+$ComputK <*Community Build>g%10,6[+$Sports*Software RecommendZ~|9`Sound Design*ComputZ~al <%3,7:Japanese/%5,8[7,5:Puzzl>g%8,5:Econom's*Express~Eng>e AnswK|6,5[9,4[7`Freelanc>g*History%10,6:Italian/%6`Parent>g*Astronomy%6,7[9`RevKse Eng>eK>g*Robot'|10,8[+$Polit's*Pet|12,5:PKsonal Productivity*Phys'al Fitness$);}}";foreach(var s in "~ion;|s%;`,4:;&Stack OvKflow;_ & ;^#3?;]7,7;'ic;['!;Zat;Ker;@6,6;>in;<Science;:'$;/ Language;+0,0#3?;*$:$;'#7?;%$:!;$\";#).B%9<;!b.GetPixel(".Split(';'))c=c.Replace(s[0]+"",s.Substring(1));new Microsoft.CSharp.CSharpCodeProvider().CompileAssemblyFromSource(new CodeDom.Compiler.CompilerParameters("mscorlib.dll System.Core.dll System.Drawing.dll".Split()),c).CompiledAssembly.CreateInstance("p").GetType().GetMethod("c").Invoke(c,null);}}}
My solution doesn't use hashing, it actually examines the individual pixels of the image and decides based on that. I discovered that it was enough to examine the blue component of the image modulo 9. The idea is to repeatedly split based on the value of pixel.B%9, like so:
b.GetPixel(3,4).B % 9 < 7 ? "Russian Language" : (b.GetPixel(8,4).B % 9 < 6 ? "Project Management" : "Philosophy")
Using a script, I generated the following monstrous program (5197 bytes) that solves the problem using a binary decision tree:
using System;using System.Drawing;class p {public static void c(){var b=(Bitmap)Bitmap.FromFile(Console.ReadLine());Console.Write(b.GetPixel(4,5).B%9<6?b.GetPixel(1,1).B%9<5?b.GetPixel(1,10).B%9<1?b.GetPixel(3,4).B%9<1?b.GetPixel(2,8).B%9<2?b.GetPixel(0,0).B%9<3?b.GetPixel(3,10).B%9<8?"Super User":"Travel":b.GetPixel(0,2).B%9<3?"Salesforce":"Craft CMS":b.GetPixel(2,4).B%9<2?b.GetPixel(2,2).B%9<6?"Ask Ubuntu":"Ask Different":b.GetPixel(1,3).B%9<6?"Mathematics":"Programmers":b.GetPixel(2,7).B%9<3?b.GetPixel(2,4).B%9<1?b.GetPixel(2,8).B%9<2?"Database Administrators":"Christianity":b.GetPixel(0,1).B%9<3?"TeX - LaTeX":"Game Development":b.GetPixel(1,6).B%9<3?b.GetPixel(2,3).B%9<7?"English Language & Usage":"Skeptics":b.GetPixel(0,0).B%9<3?"StackApps":"Unix & Linux":b.GetPixel(0,6).B%9<1?b.GetPixel(1,4).B%9<2?b.GetPixel(1,5).B%9<3?b.GetPixel(0,4).B%9<1?"Arqade":"Mi Yodeya":b.GetPixel(1,6).B%9<6?"Drupal Answers":"User Experience":b.GetPixel(1,5).B%9<4?b.GetPixel(1,6).B%9<3?"SharePoint":"Bicycles":b.GetPixel(0,0).B%9<3?"Home Improvement":"Photography":b.GetPixel(0,0).B%9<3?b.GetPixel(0,7).B%9<2?b.GetPixel(0,1).B%9<1?"Science Fiction & Fantasy":"Theoretical Computer Science":b.GetPixel(0,4).B%9<2?"Android Enthusiasts":"Ask Patents":b.GetPixel(5,15).B%9<3?b.GetPixel(2,0).B%9<3?"Meta Stack Exchange":"Stack Overflow inJapanese":b.GetPixel(0,13).B%9<7?"Stack Overflow":"Stack Overflow in Portuguese":b.GetPixel(5,8).B%9<7?b.GetPixel(4,4).B%9<7?b.GetPixel(0,0).B%9<3?b.GetPixel(7,5).B%9<7?b.GetPixel(0,1).B%9<5?"German Language":"Server Fault":b.GetPixel(8,5).B%9<7?"Economics":"ExpressionEngine Answers":b.GetPixel(1,13).B%9<7?b.GetPixel(0,1).B%9<7?"Ebooks":"MathOverflow":b.GetPixel(7,5).B%9<7?"Buddhism":"Earth Science":b.GetPixel(6,6).B%9<7?b.GetPixel(4,6).B%9<7?b.GetPixel(3,6).B%9<7?"Poker":"Gardening & Landscaping":b.GetPixel(0,0).B%9<3?"Sustainable Living":"Startups":b.GetPixel(7,6).B%9<7?b.GetPixel(0,0).B%9<3?"Quantitative Finance":"Arduino":b.GetPixel(9,4).B%9<7?"Chemistry":"Cryptography":b.GetPixel(5,4).B%9<7?b.GetPixel(9,5).B%9<7?b.GetPixel(10,8).B%9<7?b.GetPixel(0,0).B%9<3?"Reverse Engineering":"Pets":b.GetPixel(12,5).B%9<7?"Personal Productivity":"Physical Fitness":b.GetPixel(6,7).B%9<7?b.GetPixel(3,4).B%9<7?"Tor":"Robotics":b.GetPixel(7,5).B%9<7?"Politics":"French Language":b.GetPixel(0,1).B%9<3?b.GetPixel(9,5).B%9<7?b.GetPixel(3,4).B%9<3?"LEGO Answers":"Magento":b.GetPixel(6,5).B%9<7?"Motor Vehicle Maintenance & Repair":"Network Engineering":b.GetPixel(2,6).B%9<7?b.GetPixel(0,0).B%9<7?"Programming Puzzles & Code Golf":"History of Science and Math":b.GetPixel(0,2).B%9<7?"Mathematics Educators":b.GetPixel(1,4).B%9<7?"Signal Processing":"Cognitive Sciences":b.GetPixel(3,6).B%9<7?b.GetPixel(4,6).B%9<5?b.GetPixel(5,8).B%9<5?b.GetPixel(6,5).B%9<7?b.GetPixel(9,8).B%9<7?b.GetPixel(1,1).B%9<7?"Geographic Information Systems":"Biblical Hermeneutics":b.GetPixel(11,6).B%9<7?"Board & Card Games":"Bitcoin":b.GetPixel(0,0).B%9<3?b.GetPixel(2,4).B%9<7?"RaspberryPi":"English Language Learners":b.GetPixel(8,5).B%9<7?"Emacs":"Expatriates":b.GetPixel(5,4).B%9<6?b.GetPixel(6,8).B%9<7?b.GetPixel(3,4).B%9<7?"Russian Language":"Amateur Radio":b.GetPixel(8,4).B%9<7?"Project Management":"Philosophy":b.GetPixel(0,7).B%9<7?b.GetPixel(1,1).B%9<7?"Cross Validated":"Homebrewing":b.GetPixel(0,1).B%9<7?"Web Applications":"Biology":b.GetPixel(3,4).B%9<7?b.GetPixel(0,2).B%9<3?b.GetPixel(1,7).B%9<6?b.GetPixel(1,6).B%9<6?"WordPress Development":"Electrical Engineering":b.GetPixel(1,1).B%9<7?"Physics":"Windows Phone":b.GetPixel(1,0).B%9<7?b.GetPixel(0,0).B%9<3?"Webmasters":"Academia":b.GetPixel(3,8).B%9<7?"Data Science":"Worldbuilding":b.GetPixel(6,6).B%9<7?b.GetPixel(5,6).B%9<7?b.GetPixel(0,1).B%9<7?"Genealogy & Family History":"Anime & Manga":b.GetPixel(6,9).B%9<7?"Software Quality Assurance & Testing":"Open Data":b.GetPixel(9,4).B%9<7?b.GetPixel(0,0).B%9<3?"Code Review":"Community Building":b.GetPixel(8,4).B%9<7?"Chinese Language":"Computer Science":b.GetPixel(5,6).B%9<6?b.GetPixel(4,4).B%9<7?b.GetPixel(9,8).B%9<7?b.GetPixel(10,6).B%9<7?b.GetPixel(0,0).B%9<3?"Sports":"Software Recommendations":b.GetPixel(1,1).B%9<7?"Information Security":"Sound Design":b.GetPixel(3,5).B%9<7?b.GetPixel(8,4).B%9<7?"Space Exploration":"Computational Science":b.GetPixel(0,0).B%9<3?"Tridion":"Puzzling":b.GetPixel(0,5).B%9<3?b.GetPixel(6,8).B%9<7?b.GetPixel(5,8).B%9<7?"Blender":"Writers":b.GetPixel(6,5).B%9<7?"Music, Practice & Theory":"Islam":b.GetPixel(0,1).B%9<3?b.GetPixel(0,4).B%9<7?"Mathematica":"The Workplace":b.GetPixel(0,0).B%9<3?"Linguistics":"Hinduism":b.GetPixel(6,4).B%9<5?b.GetPixel(9,8).B%9<7?b.GetPixel(3,7).B%9<7?b.GetPixel(0,0).B%9<3?"Japanese Language":"Aviation":b.GetPixel(7,6).B%9<7?"History":"Italian Language":b.GetPixel(9,4).B%9<7?b.GetPixel(5,3).B%9<7?"Chess":"Freelancing":b.GetPixel(0,0).B%9<3?"Parenting":"Beer":b.GetPixel(0,5).B%9<1?b.GetPixel(4,8).B%9<7?b.GetPixel(1,1).B%9<7?"Role-playing Games":"Movies & TV":b.GetPixel(6,8).B%9<7?"Astronomy":"The Great Outdoors":b.GetPixel(0,4).B%9<3?b.GetPixel(0,6).B%9<7?"SeasonedAdvice":"Personal Finance & Money":b.GetPixel(0,0).B%9<3?"Graphic Design":b.GetPixel(3,4).B%9<7?"Video Production":"Joomla");}}
Some people have used built-in compression functions in their solutions. I made my own, writing a script that identifies common substrings and replaces them by single-character shorthands. The code is compressed to the following 2502 bye string:
us@g System;us@g System.Draw@g;class p {publ| st^| void c(){var b=(Bitmap)Bitmap.FromFile(Console.ReadL@e());Console.Write(!4,5#6?!1,1#5?!1,10#1?!3`#1?!2,8#2?*!3,10#8?$Sup] Us]+Travel~0,2_$Salesforce+Craft CMS~2`#2?!2,2#6?$Ask Ubuntu+Ask Diff]ent~1,3#6?$M^hem^|s+Programm]s~2,7_!2`#1?!2,8#2?$D^abase Adm@istr^ors+Christianity~0,1_$TeX - LaTeX+Game Development~1,6_!2,3[English/:Usage+Skept|s'*$StackApps+Unix:L@ux~0,6#1?!1`#2?!1,5_!0`#1?$Arqade+Mi Yodeya~1,6#6?$Drupal Answ]s+Us] Exp]ience~1,5#4?!1,6_$SharePo@t+B|ycles'*$Home Improvement+Photography'*!0,7#2?!0,1#1?$> F|tion:Fantasy+Theoret|al Comput] >~0`#2?$Android Enthusiasts+Ask P^ents~5,15_!2,0_$Meta Stack Exchange+Stack Ov]flow @Japanese~0,13[Stack Ov]flow+Stack Ov]flow @ Portuguese~5,8<4`%*!7,5<0,1#5?$G]man/+S]v] Fault~8,5[Econom|s+ExpressionEng@e Answ]s~1,13<0,1[Ebooks+M^hOv]flow~7,5[Buddhism+Earth >~6,6<4,6<3,6[Pok]+Garden@g:Landscap@g'*$Susta@able Liv@g+Startups~7,6%*$Quantit^ive F@ance+Ardu@o~9`[Chemistry+Cryptography~5`<9,5<10,8%*$Rev]se Eng@e]@g+Pets~12,5[P]sonal Productivity+Phys|al Fitness~6,7<3`[Tor+Robot|s~7,5[Polit|s+French/~0,1_!9,5<3`_$LEGO Answ]s+Magento~6,5[Motor Veh|le Ma@tenance:Repair+Network Eng@e]@g~2,6<0,0[Programm@g Puzzles:Code Golf+History of > and M^h~0,2[M^hem^|s Educ^ors~1`[Signal Process@g+Cognitive >s~3,6<4,6#5?!5,8#5?!6,5<9,8<1,1[Geograph| Inform^ion Systems+Bibl|al H]meneut|s~11,6[Board:Card Games+Bitco@'*!2`[Raspb]ryPi+English/ Learn]s~8,5[Emacs+Exp^ri^es~5`#6?!6,8<3`[Russian/+Am^eur Radio~8`[Project Management+Philosophy~0,7<1,1[Cross Valid^ed+Homebrew@g~0,1[Web Appl|^ions+Biology~3`<0,2_!1,7#6?!1,6#6?$WordPress Development+Electr|al Eng@e]@g~1,1[Phys|s+W@dows Phone~1,0%*$Webmast]s+Academia~3,8[D^a >+Worldbuild@g~6,6<5,6<0,1[Genealogy:Family History+Anime:Manga~6,9[Software Quality Assurance:Test@g+Open D^a~9`%*$Code Review+Community Build@g~8`[Ch@ese/+Comput] >~5,6#6?!4`<9,8<10,6%*$Sports+Software Recommend^ions~1,1[Inform^ion Security+Sound Design~3,5<8`[Space Explor^ion+Comput^ional >'*$Tridion+Puzzl@g~0,5_!6,8<5,8[Blend]+Writ]s~6,5[Mus|, Pract|e:Theory+Islam~0,1_!0`[M^hem^|a+The Workplace'*$L@guist|s+H@duism~6`#5?!9,8<3,7%*$Japanese/+Avi^ion~7,6[History+Italian/~9`<5,3[Chess+Freelanc@g'*$Parent@g+Be]~0,5#1?!4,8<1,1[Role-play@g Games+Movies:TV~6,8[Astronomy+The Gre^ Outdoors~0`_!0,6[SeasonedAdv|e+P]sonal F@ance:Money'*$Graph| Design~3`[Video Production+Joomla$);}}
The dictionary needed for decompression is just 108 bytes:
: & ;<%!;|ic;`,4;_#3?;^at;]er;[%$;@in;>Science;~'!;/Language;+'$;*!0,0#3?;'$:;%#7?;$\";#).B%9<;!b.GetPixel(
The dictionary uses semicolons as delimiter, and contains single characters followed by their decompression. So to decompress, ":" would first be replaced by " & ", then "<" by "%!", "|" by "ic", and so on. Decompression of a string c can be expressed in quite a concise way:
foreach (var s in "[dictionary]".Split(';')) c = c.Replace(s[0] + "", s.Substring(1));
Then, after decompression I use some reflection black-magic to compile the code on the fly and run it:
namespace System
{
using Collections.Generic;
using CodeDom.Compiler;
using Microsoft.CSharp;
using Linq;
using Reflection;
class P
{
static void Main()
{
var c = "us@g System;us@g System.Draw@g;class p {publ| st^| void c(){var b=(Bitmap)Bitmap.FromFile(Console.ReadL@e());Console.Write(!4,5#6?!1,1#5?!1,10#1?!3`#1?!2,8#2?*!3,10#8?$Sup] Us]+Travel~0,2_$Salesforce+Craft CMS~2`#2?!2,2#6?$Ask Ubuntu+Ask Diff]ent~1,3#6?$M^hem^|s+Programm]s~2,7_!2`#1?!2,8#2?$D^abase Adm@istr^ors+Christianity~0,1_$TeX - LaTeX+Game Development~1,6_!2,3[English/:Usage+Skept|s'*$StackApps+Unix:L@ux~0,6#1?!1`#2?!1,5_!0`#1?$Arqade+Mi Yodeya~1,6#6?$Drupal Answ]s+Us] Exp]ience~1,5#4?!1,6_$SharePo@t+B|ycles'*$Home Improvement+Photography'*!0,7#2?!0,1#1?$> F|tion:Fantasy+Theoret|al Comput] >~0`#2?$Android Enthusiasts+Ask P^ents~5,15_!2,0_$Meta Stack Exchange+Stack Ov]flow @Japanese~0,13[Stack Ov]flow+Stack Ov]flow @ Portuguese~5,8<4`%*!7,5<0,1#5?$G]man/+S]v] Fault~8,5[Econom|s+ExpressionEng@e Answ]s~1,13<0,1[Ebooks+M^hOv]flow~7,5[Buddhism+Earth >~6,6<4,6<3,6[Pok]+Garden@g:Landscap@g'*$Susta@able Liv@g+Startups~7,6%*$Quantit^ive F@ance+Ardu@o~9`[Chemistry+Cryptography~5`<9,5<10,8%*$Rev]se Eng@e]@g+Pets~12,5[P]sonal Productivity+Phys|al Fitness~6,7<3`[Tor+Robot|s~7,5[Polit|s+French/~0,1_!9,5<3`_$LEGO Answ]s+Magento~6,5[Motor Veh|le Ma@tenance:Repair+Network Eng@e]@g~2,6<0,0[Programm@g Puzzles:Code Golf+History of > and M^h~0,2[M^hem^|s Educ^ors~1`[Signal Process@g+Cognitive >s~3,6<4,6#5?!5,8#5?!6,5<9,8<1,1[Geograph| Inform^ion Systems+Bibl|al H]meneut|s~11,6[Board:Card Games+Bitco@'*!2`[Raspb]ryPi+English/ Learn]s~8,5[Emacs+Exp^ri^es~5`#6?!6,8<3`[Russian/+Am^eur Radio~8`[Project Management+Philosophy~0,7<1,1[Cross Valid^ed+Homebrew@g~0,1[Web Appl|^ions+Biology~3`<0,2_!1,7#6?!1,6#6?$WordPress Development+Electr|al Eng@e]@g~1,1[Phys|s+W@dows Phone~1,0%*$Webmast]s+Academia~3,8[D^a >+Worldbuild@g~6,6<5,6<0,1[Genealogy:Family History+Anime:Manga~6,9[Software Quality Assurance:Test@g+Open D^a~9`%*$Code Review+Community Build@g~8`[Ch@ese/+Comput] >~5,6#6?!4`<9,8<10,6%*$Sports+Software Recommend^ions~1,1[Inform^ion Security+Sound Design~3,5<8`[Space Explor^ion+Comput^ional >'*$Tridion+Puzzl@g~0,5_!6,8<5,8[Blend]+Writ]s~6,5[Mus|, Pract|e:Theory+Islam~0,1_!0`[M^hem^|a+The Workplace'*$L@guist|s+H@duism~6`#5?!9,8<3,7%*$Japanese/+Avi^ion~7,6[History+Italian/~9`<5,3[Chess+Freelanc@g'*$Parent@g+Be]~0,5#1?!4,8<1,1[Role-play@g Games+Movies:TV~6,8[Astronomy+The Gre^ Outdoors~0`_!0,6[SeasonedAdv|e+P]sonal F@ance:Money'*$Graph| Design~3`[Video Production+Joomla$);}}";
foreach (var s in ": & ;<%!;|ic;`,4;_#3?;^at;]er;[%$;@in;>Science;~'!;/ Language;+'$;*!0,0#3?;'$:;%#7?;$\";#).B%9<;!b.GetPixel(".Split(';')) c = c.Replace(s[0] + "", s.Substring(1));
var o = new CSharpCodeProvider().CompileAssemblyFromSource(new CompilerParameters("mscorlib.dll System.Core.dll System.Drawing.dll".Split()), c).CompiledAssembly.CreateInstance("p").GetType().GetMethod("c");
o.Invoke(o, null);
}
}
}
Note that the examples used here for explanation are slightly different from the one used in the 2876 byte solution.
I wonder how many of those sites still have the same favicon 3 year's later... – caird coinheringaahing – 2018-03-30T15:58:13.127
5CRC32 is shorter than MD5. Anyone who knows an even shorter checksum algorithm will probably win. – manatwork – 2014-12-08T13:14:55.270
@manatwork You'd still have to turn that into a short value to look up the strings and compress the lookup table. And I'd wager that writing your own clever hash in a terse language could be shorter than calling a built-in hashing function and shortening the resulting hash in a "normal" language. – Martin Ender – 2014-12-08T13:18:11.163
What is the expected behavior in case of no matching site is found? Or should we assume the image will be always a valid site icon? – manatwork – 2014-12-08T15:40:36.340
@manatwork Yes, you can assume that the input will be one of those 132 images. – Martin Ender – 2014-12-08T15:42:26.680
Do we need to examine the actual pixels, or is it sufficient to generate a hash from the raw PNG data? – r3mainer – 2014-12-08T16:54:03.723
1@squeamishossifrage You may generate a hash from the pixel values. I don't know how flexible the PNG format is, but whatever format you choose, if there are two different files that encode the exact same image, your program has to work for both of them. So you might not be able to make any assumptions about the precise byte stream from the image file, other than it's a valid image in whatever format you chose. I should clarify that. – Martin Ender – 2014-12-08T16:57:07.070
1@MartinBüttner Yes there can be two different PNGs that encode the same image, otherwise
pngcrushwill not exist. – kennytm – 2014-12-08T17:14:12.2701I feel that this could be done amazingly with a decision tree that analyses pixels at specific co-ordinates in the image... I'm sure there's some simple ML technique to identify the "key features" that can be used to distinguish the images... Time to dig out my ML notes! – Mark K Cowan – 2014-12-08T21:51:46.177
1@MarkKCowan Look at my solution, I basically do that. For every pixel, I make a list of the different color values it has in all the images. Then I pick the median value, and split the images on two depending on their color in that pixel. Then do the same recursively to the two halves until you're down to a single image. – Tom van der Zanden – 2014-12-09T13:39:52.073
@TomvanderZanden: Nice, binary search on images :D Somewhat simpler and more elegant than my idea, for pretty much the same effect! – Mark K Cowan – 2014-12-09T13:54:25.700
@Martin, I found that the icons of Earth Science and Spanish Language have different bitmaps. The CRC32 of the pixel arrays are different. But as far as I can tell, the pixels for Magento and Martial Arts are identical as you have stated. – Logic Knight – 2014-12-10T08:59:15.010
@CarpetPython Yes, Earth Science and Spanish Language are different when taking the alpha channel into account. I had intended to remove the alpha channel, but I messed that up, so those two are actually distinguishable. – Martin Ender – 2014-12-10T09:01:11.010
How long did it take to make this post with all those image files? – TheDoctor – 2014-12-10T14:58:46.147
Optimizer wrote a JS snippet to scrape all their URLs. Then I wrote a script in Mathematica to download them, extract the 16x16 version and save them as PNGs with the correct file name on my hard drive. And then, yes, I had to drag and drop all 132 of them one by one into the browser window so SE uploads them to imgur. – Martin Ender – 2014-12-10T15:07:39.713