Introduction:
Quick post for posterity sake. This also started from TvojaStara's posts back when bumex had just started to convert outfits. TvojaStara had a great character that had some interesting Tattoo's in here http://www.loverslab.com/topic/72183-fo4-clothing-conversions-from-skyrim-wip/page-17? also here: https://postimg.org/image/en8a4o9vn/

I pm'd and asked what those were and TvojaStara responded: "tattoos are from a skyrim mod called "Corintio's Progressive Slavetats 0.04b" you can find it on LL"
the first thing I noticed was that all the Tattoos were .dds files, which isn't a simple drop click on this to add to NMM to my dismay. I took a pretty long break from Fallout, but recently returned and realized I wanted them.

Instructions:
First you need a program that can open .dds files, there a bunch that do it, but the easiest (and cheapest) option is to use Gimp. There is a great steam thread that covers this here: http://steamcommunity.com/sharedfiles/filedetails/?id=816839147

1. Get GIMP (https://www.gimp.org/)
2. Then get gimp-dds ( https://code.google.com/archive/p/gimp-dds/downloads) - gimp-dds 3.0.1 (Windows 64-bit binaries)
3. You install it by adding it into the plug-ins folder. This allows you to open .dds files
4. The next thing I realized is I don't want everyone to have tattoos, sooooo looks like I needed Unique Player (https://www.nexusmods.com/fallout4/mods/3718/?) which I hadn't really found a need for until then.
5. Go get the female body .dds (femalebody_d.dds) from Data\Textures\Actors\Character\PlayerHumanFemale
6. You then open femalebody_d.dds (see note below), and the Open the other .dds tattoos as layers, now you can edit it and place them wherever you want. I created several "Layer Groups"
7. Save this project as a .xcf so you can always open it later
8. When you finally have the skin you want, [Flatten Image] and then Export with the settings below
   

Gimp Options:

• When you open the .dds you get a prompt, [uncheck] Load mipmaps
• During Export: Compression BC3/DXT5, Mipmaps: [Generate mipmaps] [Check] Use Perceptual error metric
  

Great Tattoo Resources

The best and easiest thing to do to get great tattoos is to use all those created for Skyrim. As a quick note, if you import a texture that is low res, put them all into the same layer group, and from the Gimp menu bar, use the scale transform option to get them the right size.

Here are the ones I found I enjoy

Scratch Slavetats 1.02
Body Graffiti SlaveTats Pack Added Pricelist
SlaveTats Cane Marks 1.1
Corintio's Progressive Slavetats 0.04b