Moved to DAZ Studio Discussions - Developer Discussions is for scripting.
You can’t paint inside DAZ Studio, but if you have images you want to apply you can do so (to an extent) with the Layered Image Editor - it won’t freely rotate the images, and it won’t split them across seams, but it can help. Alternatively you would make a copy of the texture file and add the detailing in another application - an image editor or a 3D paint tool.
To use the Layered Image Editor you need to apply the base texture, then open the Surfaces pane (Window>Panes(Tabs)>Surfaces) and select teh surface to which you want to apply the tattoo or scar. Click the little thumbnail next to the Diffuse colour slider and from the menu select Layered Image editor. That should open a dialogue showing the applied texture in the window on the left, with it’s name at top-right. Click the + under the panel with the name and select Add Layer. Make sure the new layer is selected and click the resource button, then select browse and load your tattoo image. You should be able to drag and scale the new layer around to position it,