PHM_00_Customizing_Head_Tattoo_0001.dds
PHM_00_Customizing_Body_Tattoo_0001.dds
PHW_00_Customizing_Head_Tattoo_0001.dds
PHW_00_Customizing_Body_Tattoo_0001.dds
PEW_00_Customizing_Head_Tattoo_0001.dds
PEW_00_Customizing_Body_Tattoo_0001.dds
PGM_00_Customizing_Head_Tattoo_0001.dds
PGM_00_Customizing_Body_Tattoo_0001.dds
PBW_00_Customizing_Head_Tattoo_0001.dds
PBW_00_Customizing_Body_Tattoo_0001.dds
PNW_00_Customizing_Head_Tattoo_0001.dds
PLW_00_Customizing_Head_Tattoo_0001.dds
PGW_00_Customizing_Head_Tattoo_0001.dds
PGW_00_Customizing_Body_Tattoo_0001.dds
You can also edit the .dds for the bodies (search for *nude*.dds) in the character/texture folder. phw_01_nude_0001.dds is used by most female humans, pww_01_nude_0001.dds for witch, pew_01_nude_0001.dds for ranger, pbw_00_nude_0001.dds for tamer plw_00_nude_0001.dds for Shai, pdw_00_nude_0001.dds for Dark Knight, pfw_01_nude_0001.dds for corsair and I think Drakania shares phw as well. you have to create a new layer in Gimp and add your tatoos, save the work in progress in whatever extension gimp uses in case you need to make adjustments.
You can use the customizing tattoos as base to figure out where each body part ends.
When you're ready to test out your art, merge down the tattoos onto the body and export as dds (DTX1 compression I think), overwriting the original one.
the first time around you're likely to have the tats at the wrong place, that's why it's best to save the "work in progress" with the gimp extension so you can easily move the tats around and re-merge down before re-exporting as dds.
Make sure the file sizes are the same, size difference sometimes means that you messed up the original size of the image and it will be all transparent in game.
hope this helps.
P.S. you can also change the worker icons by replacing the files in \Paz\files_to_patch\ui_texture\new_ui_common_forlua\widget\worldmap\workericon
:)