The only thing that will really blend into/onto chocolate is more chocolate or cocoa butter. Obviously, you can stick any image onto a piece of chocolate, probably even an edible image frosting sheet by just warming the surface of the chocolate as you are ready to apply the image. I've never had chocolate with either a frosting sheet image on it, or a wafer paper image. I can tell you that wafer paper is bland and somewhat crunchy (they make communion hosts out of the same thing). I'm not sure that either would "compliment" the chocolate very well.
Chocolate transfers are made, as ShirleyW said, of colored cocoa butter printed on acetate sheets. You pour warm chocolate over the transfer and after the chocolate sets up, you peel off the acetate and the image remains on the chocolate piece.
You can have custom made chocolate transfer sheets made, but the cost is usually very prohibitive. There's a set-up fee and a minimum order fee. The example below is from sugarcraft.com
http://www.sugarcraft.com/catalog/candies/transfersheets.htm#custom
Custom 12x16 inch Transfer Sheets - 300 sheet minimum ($2.75 per sheet) one color $825.00
Set-up plate charge (one-time charge) $150.00
The chocolate "transfers" often referred to here on CC are images outlined and filled in using melted chocolate. Once the piece sets up, it's set on/on top of a cake, etc.
HTH
Rae
