What can I put over a candle to protect a picture from scratching off?

I run a small business out of my house. One of the items I sell are personalized candles. I print out a picture on a special sheet of paper that turns in to a film that can be applied over the candle. I can print text, pictures, anything the customer wants. The problem is that the film, once dried, can easily be scratched and rubbed off with regular or basic handling. Is there anything I can put over the candle that is non-flammable to protect the image, but still allow the candle to burn down properly (and not ignite the customer's coffee table)?