Just to toot my own horn, here was a script I wrote using Bagginsbill's Matmatic
and Parmatic put a tattoo on Jessi.  It lets you add a tattoo and a skin texture and
then creates parameter dials that let you scale the tattoo in the x and y direction
and move it in the x and y direction.  Makes it a lot more simple than fooling around
with Photoshop or messing around with blender nodes.
Just cut and paste below to notepad and save it as tatto.mm1.txt
Then fire up Matmatic to create your MT5 file, apply it to your character,
run Parmatic, and start spinning them dials.

 
# You'll need to supply your own tattoo.  
# And the proper directory path.  
# Make sure the background of the tattoo is white  
# or it won't work.  
# But this will let you easily scale and locate the tattoo  
# If you want to use it on another character, substitute that  
# character's texture map and directory path.  
        
cx = Add(.4).labelled('PM:xloc')        # X offset parameter dial  
cy = Add(.4).labelled('PM:yloc')        # y offset parameter dial  
xscale = Add(.2).labelled('PM:Xscale')  # scale parameter dial  
yscale = Add(.4).labelled('PM:Yscale')  # scale parameter dial  
 
tat = ImageMap("Mystuff:Runtime:Textures:Tattoos:Chinese Dragon color.png")  
tat.U_Offset = cx  
tat.V_Offset = cy  
tat.U_Scale = xscale  
tat.V_Scale = yscale  
tat.Image_Mapped = 0  
 
clr = ImageMap("Poser 6:Runtime:Textures:Poser 6 Textures:Jessi_Body.jpg")  
 
clr = Color_Mul(clr, tat)    # Combine the skin texture with the tattoo  
 
s = Surface()            # Set up the Surface  
s.Diffuse_Color = clr  
s.Specular_Color = BLACK