I think there would be more of a market for putting peoples own pics in mugs
I actually like that idea too, think of the shock when some ones face appears when you have just swigged your last bit of tea!
One point, there are many people trying to get a bit of an income from all sorts of things, its a simple equation, look at the cost and then then selling price, then I think the key issue is marketing, you can sell anything, if you do the right sort of marketing to the target group!! Know your market!