1. picks one incantation randomly for each display 2. slightly and randomly alters the position/rotation of each character 3. adds a tiny blotch now and then
Like the print in a real book, especially ones printed before 1970.
I also suggest that the background be an actual scanned image of a blank piece of paper. Those "paper color" backgrounds are too perfect. Take some blank pages out of an older book sometime and scan them, and you'll see what I mean.