I did it with a JavaScript JPG encoder - not randomly flipping output bits, but randomly flipping bits during the encoding: http://www.mrspeaker.net/dev/jpgcrunk/
(Though I kind of have a feeling I pushed my project when this article was posted originally! [Edit: ha, yep, I sure did - someone linked the original discussion below])
(Though I kind of have a feeling I pushed my project when this article was posted originally! [Edit: ha, yep, I sure did - someone linked the original discussion below])