You choose one, and "copy" it - which could mean redrawing it from scratch, or modifying some section of it, or whatever. The end result is a picture of the same size that should bear a strong resemblance (in some way) to the original.
You submit your new copy of the picture.
But what's actually happening is that these pictures are part of a larger picture, and so people are collectively redrawing different quarters of the one picture, which are in turn divided up, etc. The end result? To be honest, I'm not real sure.