piping gel or the toothpick method. (poking holes into wax paper then putting wax paper on top of cake and pressing to make the holes imprint on cake...and then do dot to dot or sprinkle powdered cocoa, sugar into holes while on cake.... kind of like a stencil)
my husband bought me a Projecta Scope w/extention arm to clamp to a table. You can put small pictures of almost any clip art color or black and white in it and project it on top of the cake. I did a bridal shower sheet cake that way. It had two flying doves holding a ribbon between them. I outlined it with #3 tip and buttercreme icing for writing. Then I filled in similar to doing character cakes.