Copyright Question

Just a quick post, to see if anyone knows the answer to this one. While I was in the shower this morning, a place I find I frequently get inspiration (anyone else?), I had the thought that the ancient Roman mosaics I've been seeing in the museums here in Italy would make really awesome cross stitch patterns. I wouldn't feed my photos into a program if I were going to do this, I'd design them by hand. Does anyone know how the copyright would work on something like that? My guess is that if I'm working from a photograph I took and creating a (even very similar) pattern, it shouldn't be an issue, the moreso because there is certainly no copyright on two thousand year old mosaics, but I know from experience that when museums get involved these things can get fuzzy. Thoughts?

Here are a couple of examples (because all posts are more fun when they have pictures!):