Have a look also at Bump Mapping...
You can create a bump map of the target region and then apply the bump map as a distortion to the tattoo... The result will be a perfect match!
Here are a couple of tutorials that explain the process fairly well:
Wrapping objects with Displacement Maps in Photoshop (Probably all you'll need)
Photoshop Displacement Map Example
A couple of notes about bump maps (or disaplacement maps):
1. When you save your map, make sure it's in .PSD format\
2. Make sure to save your map near the top of your folders... Photoshop will not work if the full path name to the map is too long but does not give you an error message.
Hope this helps,
Mike.