Open desired Photos in Photoshop, I will use below pictures,
Using magic erase Tool we are going to remove tatoo background
Select Magic Erase Tool then click on the tattoo background
This is how the image will appear after removing the background
Select Move tool, and drag a tattoo into your photo
Now tattoo and the photo will be on the same document, after that then delete original tattoo image
you will remain with your Photo and tatoo image on top of it
Resize tattoo image by pressing ctrl+T on the keyboard, when done with resizing,moving and rotating press enter
To resize even better, go to Edit - transform - perspective then you can continue positing the tattoo until you are satsified with the result, when done press enter
Now change blending mode to multiply,play around with opacity until you are sastified with the result
Now go to Image- Adjustments- Levels. Play with black and white settings as you desire then click OK
Here is my final result