do you have to have fondant under edible pictures on a three layer cake?
No,the pics can be placed right on to buttercream icing, but in my opinion, even if I had an iced cake, I would make some thin fondant and adhere the pics to that. You can do this by slightly dampening the fondant, SLIGHTLY, and sticking the photos on, then leave a small border of fondant by trimming around them. I think this looks really professional.
Hope this helps -
You can put edible pictures on just about anything that is smooth an has some dampness to it. If it is not damp, dampen it with a damp paper towel or a fine mist of water.
I've put mine on fondant and on buttercream. If you are putting it on a color icing, I would back it with a thin layer of fondant like Jennifer suggested. I use piping gel.