For most of these I used Paul Hertz's glitch art program that he wrote in Java (I forget the name, but it is available for download on his ignofactory website). I am also working on my own program to do things like pixel-sorting with precision by manually specifying the beginning, end, and sort type as a script or via a gui.
@thufir This is cool! I've wanted to use Processing to create something too.
This gave me an idea. What if you train a neural network to glitch some images, with you selecting the 'winner' of each round, thereby training the system to find which portions of the file to corrupt to result in desirable glitch art.