Build an image-glitching algorithm

Question

It's well known that corrupted JPEG files or NTSC/PAL streams will appear as distorted versions of the true images, or versions covered in random-looking blocks of pixels.

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Consider the below image (from here):

If we run it through this filter (with settings 44, 7, 21, 83, for anyone who wants to reproduce it), it ends up looking like this:

Your task is to build a program that takes the pixels of a given image and mutilate it in some way to make it look like a computer processing error like above.

Your program will take an uncompressed bitmap file (in the format of your choice) and return a "glitched" file of the same uncompressed format.

Your program may not make any use of existing image processing libraries. (This is to make sure that the algorithm does not simply flip a few bytes in the file and let the image decompressor do the rest, like JPEG glitch programs usually do.)

Your program must also visibly transform existing pixels, rather than simply overlaying noise on the picture.

As this is a popularity contest, the program with the highest votes is the winner.