How much effort need it be? Consider a convention that prints all the badges on the spot (as a number do now, with varying degrees of appropriate technology). Adding a digital camera to the process needn't be that expensive: 1 extra staffer to do it, the camera is borrowed and tethered, and since the badge is being computer-generated and printed on the spot, no other extra effort.

If the person's name is printed in large clear type, then clearly "identifying to others" is an important point.

Suppose that were the most important issue, and preventing badge sharing/stealing were a close second. How would you do the latter?