I had a rather spontanious thought the other day. In the wizarding world, we know that photographs can move and that illistrations can move, but I wonder about tattoos. In the movies, we see that Sirius has a great many prison tattoos, but what I wonder is if wizarding tattoos can move the way other wizarding images can.
It certainly wouldn't make it very easy to hide if they did. A person could be in the middle of a job interview or dinner with their parents, and suddenly a Peruvian Vipertooth flies across their face and down their neck.
I wouldn't think that tattoos have the ability to move all over like that, if they can move at all. If they can move, I'd imagine that they'd be restricted to a certain amount of space/skin.
*ponders* In Tamora Pierce's Circle of Magic quartet, Briar Moss gets tattoos that move... but that's because his magic is plant based and he was stupid enough to use vegetable dyes to tattoo himself, so it's affected by his own magic. So the tattoo kinda grows and shifts but only over his hands.
Completely different series, but it was the first thing to come to mind about magical moving tattoos.
I recall Colin Creevy saying that the reason wizarding photos move is because they're processed differently. The camera itself and the film are not actually different.
*thinks some more*
Do we know anything about how the portraits are enchanted? I would guess that it's not something due to the ink but something that is enchanted after the painting is finished.
In both the cases of photos and portraits, it doesn't seem to be the ink itself. That would imply that either tattoos would have to be enchanted afterwards to move... and for obvious reasons limiting the movement of them would be a good idea.
I've certainly some HP fics with moving tattoos. (And some, I mean not nearly enough!) I think it is totally plausiable. I thought Colin talks about developing the pictures in special potions, rather than muggle chemicals so they move, or that the muggle chemicals could be altered with potions or charms? I can't remember which. But I don'tthink you cast a spell on the photo after it has been developed.
I always imagined the paint used for portraits had additonal magical ingredients or charms that meant that things painted with it move. That way you don't have to cast a spell on a painting or the paint yourself - you can just buy it already enchanted.
Basically that long paragraph what all to say I can easily imagine a wizard somewhere figured out what charms and/or potions can be added to ink to make the tattoo move. Sirius probably didn't have access to such inks in Azkaban so his prison tattoos wouldn't move. Possibly the tattoo could be restricted, or it might just be a risk that you take with a wizarding tattoo! Maybe upmarket, professional tattoo parlours can restrict the area the tattoo moves in, but cheaper places don't?
I read a lovely fic years and years ago about Luna getting a wizarding temporary tattoo - she got a tattoo of a butterfly egg that than grew and went through the butterfly lifecycle. It was easy to hide as a slow moving caterpillar, but then when it was a butterfly, it was pretty hard to keep hidden! I thought it was a lovely idea, and I am very taken with the idea of wizarding tattoos.
Like AidaLuthien said, I seem to remember reading that potions cause the photographs to move. So, if you think about it, if you mixed similar potions with tattoo ink, it should be possible to make them move. I'm not sure about restricting, though. the people in normal photos seem to restricted to frames, even if the portraits in Hogwarts often take excursions. I'm not sure if that's just a Hogwarts thing or a painting thing in general.
Actually, the wizards on the cards from chocolate frogs leave their cards, so perhaps there is a specific potion used in photos so that the subject stays in the specific area. I suppose that it really is just open to interpretation.
I agree with all the above. I think that the tatoos might also move as a result of being connected to a wizard/witch. I think in OotP, Sirius stuns the portrait of his mother, and you might be able to do something similar with tattoos. I'm not sure how that would work though. You might just end up stunning yourself.