PhotoFrost Edible Photos and Images on Cake Frosting.
Information on getting started with edible images. You can order images from your own prints, or learn how to set yourself up with the equipment to create your own.

Pictures and Photos on Cakes by Icing Images
Icing Images will scan your photo and mail your image to you as an edible cake decoration, or you can purchase supplies that will allow you to do the same thing from home.