Actually to confuse things further....

You can't copyright a photo of a 2d painting that is in the public domain.

***Bridgeman Art Library v. Corel Corp. *** was the lawsuit that said you can't claim copyright of a photographic image of a 2d painting that copyright has expired on due to the fact that there hasn't been enough original content added.

This mainly pertains to the US copyright law, you may find other countries do not allow such.

( http://en.wikipedia.org/wiki/Bridgeman_Art_Library_Ltd._v._Corel_Corporation )

So more than likely you would be absolutely fine using the images for your tattoos.

 - Noel