I draw a lot of slideshows, which are usually composited in Photoshop; each layer or layer set is eventually exported as a single slide image. I make one background at the bottom of the stack of layers, and make the art for each slide transparent so the background shows through. Here’s what happens when I get bored and make a bunch of the layers visible at the same time – maybe a dozen portrait heads in watercolor mashed together. Looks kind of like Wolverine on a caffeine binge, huh?