A cake can be decorated with a photograph by printing the photograph onto an edible icing sheet and then setting the sheet on the desired portion of the cake. The ink used for printing the photograph on the edible icing sheet is likewise edible, made from sugar and food-grade coloring.
Edible ink printing is a process in which the designs on a cake and other confectionery products are created on a computer and printed out using a stock printer with a modified cartridge that holds the edible ink. Confectionery businesses that offer edible ink printing on their products use food-grade materials that are approved by the United States Food and Drug Administration with a "generally regarded as safe" classification.
Also called frosting sheets, the icing sheets that are made with sugar and starches behave like regular paper in the way they flow through the printer and absorb the edible ink. The frosting sheets are made to blend easily into any moist surfaces, such as the icing on a cake.
The ink is a sugar-based liquid that is specially made to function like regular printer ink. It has to have small enough molecules in order for it to pass through the small nozzles of the printer. The ink cartridges that are used to modify regular printers are made with materials that are also acceptable for food contact standards.