Someone on here has done it before with a Batman themed strat, but I'm not sure what methods were employed. there's a couple of approaches but I was thinking a collage of different panels. There is a method I've seen where you can print comic panels onto normal paper with an inkjet printer, and then transfer them onto the guitar with mod podge and rub the paper away, leaving the image. The big advantages there would be that I don't need to source and cut up comics (cutting up comics feels sacrilegious to me), and I can do the entire design on the computer and do it all at once, in as flat a layer as possible. The mod podge ends up a bit bumpy but apparently you can get it fairly smooth with a whole lot of clear coats.