Do you suggest icing or fondant for edible images?
Can I create a 40 dollar bill from a graphic design program then give the image to a bakery and get a custom size edible sheet?
Any other tips/suggestions greatly appreciated
Sure, you can design a fake bill and have a bakery print it onto an edible sheet.
You will be limited to the size of edible paper they have in stock (usually the standard 8-1/2 x 11 inches). You then cut the sheet smaller if you want.
So--if your sheet cake needs to be bigger, print a few of the same bills and overlap them on the top. They will get the message across just fine.
If the customer wants regular icing, please warn them that this fancy printing job would be safer if you laid a thin sheet of fondant (waterproofing) just on top of the cake under the printed sheet(s). Work it out before you start designing.
I have seen this done before. I googled "Dollar Bill Editor" and Lunapic offered a free editor and lets you create a "real looking" bill...but it doesn't have the demonation you need. Maybe if you google some more, there may be another programs there. Try different phrases..."Dollar Bill Fun".....etc. We have such a protective fire wall here at work I couldn't try any of the sites I found. Good luck.
Those edible inks will run with humidity. Yes they are completely edible--very similar to the watery food colours you can buy in grocery stores. The "paper" is sugar with some kind of binding gum, also completely edible, but it likes to suck up water and get mushy.