The trick to it, though, is to paint it in layers, with the "front" layer painted first and the background colors painted over those. Here's my first attempt.
I will warn you, it stunk. :) But practice makes perfect.
Find a picture you like and print it.
Start filling in the smaller things, like the sun, the yellow windows and the purple detail on the roof.
I didn't get a picture of the next thing, which was, color in the main color, the black of the house. It does not matter if you get into any of the yellow, because the yellow is down on the paper first, up front. If back gets behind it, you won't see it, because the yellow is the front layer.
Once you're done, you can also add a smear of the icing that's on your cake. I figured later that this really was not needed, but every instructional I read said to.
Place your buttercream transfer in the freezer. Prepare your cake, making sure that the buttercream on the cake is firm and set. (mine was not).
After at least 15 minutes in the freezer (can make these days and days ahead of time), place the buttercream side of the wax paper down on your cake. Gently peel off the wax paper, rubbing it down if you need to loosen some of the buttercream off the wax paper.
Voila. Buttercream transfer. It's kind-of goopy, but I'm getting the idea.