Not all people self-document their clothing textures with names like "longhairTRAN.jpg" but it is usually possible to figure out what is used where by opening the image in an image editor. Of course, you can also open the item in Poser and look in the Materials editor to see what is going on. Most Poser textures, these days, consist of some number of images stored somewhere in the "textures" folder of your Runtime, and one or more "MAT" poses installed in the "poses" folder of your Runtime. The MAT pose is a third-party hack that changes materials. (These days, Poser6 gives even more options for saving materials....but MAT poses still lead in popularity.) Clothing and props packaged for Poser will usually (though not always), include a a core file in .cr2 or .pp2 format, which refers to geometry in an .obj file and image textures in JPEG format. They also, often, will make templates available for the ease of a user who wants to apply their own textures to the item.