Think of the hassle you save yourself when presented with the opportunity to try a new hairstyle before a pair of scissors gets anywhere near your head. Well, if something goes wrong despite such precautions, at least nature will sort it out in a matter of weeks. How much worse would it be if a tattoo went wrong?
I'm not a tat fan myself. Nevertheless, I think a site like Tatmash represents a great use of technology. You can upload a photo of yourself and then see what different tattoos would look like on you. I wouldn't necessarily advise you to get your students trying it out, given that you can elect to have a tattoo displayed on any part of your anatomy, but it's good to know that this facility is not only possible but also both easy and free.
What other uses might you find for this sort of thing in an educational context?