This is the finished product from this tutorial, a girl with a tattoo on her arm.
I'm going to use two pictures to do it; the girl and the tattoo:
Open the girl picture, then go to Image > Adjust > Desature. Now go to Filter > Blur > Gaussian blur. I used 1,5px for this picture.
After this, save the image as a .PSD file with the name "displace.psd"
Ok, now open the tattoo picture, go to Select > All and then Ctrl+C (to copy the image).
Now open the girl original image (without the blur, etc), and then Ctrl+V to paste the tattoo image. The tattoo image will be pasted in a new layer, call this layer "tattoo".
Now at the tattoo layer, go to Edit > Transform > Scale and put the image in the right position and scale you want. Also, change the "tattoo" layer to Linear Burn mode.
Still on the tattoo's layer, go to filter > distort > displace
Use the "displace.psd" that you saved previously.
The tattoo will adjust to the womans body, this step is not so important in this image, but becomes very important when dealing with larger tattoo on large pics.
Now, give a very small Blur on the tattoo layer, Filter > Blur > Gaussian, I used 0,2 px.
Put the 'tattoo' layer opacity (on the layers tab) to 80%.
Hover over to see "before" image.
And we are done!
I hope that you enjoyed this tutorial.
More Tutorials: 
