If you have a tattoo color map, load it into another Image_Map. Connect up this Image_Map to the same 3 math functions as before. Now you see the magic. As we move or scale the mask, we also move or scale the color map in perfect synchronization.

Change the Blender:Input_2 to white, and connect to the tattoo color map. Render. You should see a faded copy of your tattoo.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)