The position is wrong for the unimesh characters, adjust the u and v_offsets until it is in the right place on the texture. Because you have a light tattoo surrounded by black (the opposite of the tute you are using) you will need to change the background color (on the tattoo node) to black and the colormath node to add. If the add does not combine the images as desired, you may be able to use your tattoo as a mask and plug that into input 2 and the blending input of a blender node and adjust the multiplier on the blending input to 1 or more, your skin would go on input 1.