Is it possible for a download to specify it's own icon (as a file in the GUI)? So for example, if I download a file called foo.dmg can I make it show up (in the download bar or in the explorer) as a video. I'm asking for Mac but Windows would be a bonus.
Reason this is security related: I (and I'm sure others) rely on the logo to trust that the right app will be used to open the file as a proxy to checking the extension.