I discovered accidentally that emacs will load jpg files and display them. I don't know what good that does you, really. But you can use ctrl-c ctrl-c to toggle between displaying the image, and showing the raw file as text.
Which means you can garble up the image by adding or subtracting bytes and then see how damaging the file changes the image. It's kind of interesting, in an avoiding-work sort of a way. Though it seems like when I do it, everything comes out looking like a Designer Republic album cover:
This used to be the front cover image of Neu '75