The last butterfly tattoo looks more like a tattoo. yes, the image choice has something to do with it as well, but I think you have the skin overlay pretty close in the last butterfly. :)  It has that slightly blended slightly muted look that healed tatto's get :)
The girls are looking a lot more like tattoo's as well.

I'd look for some tribal or celtic weave or ornament for the testing. Might be a bit easier to get the right under the skin look witha a single color/tone image :)  HTH!

Hi, my namez: "NO, Bad Kitteh, NO!"  Whaz yurs?
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