This is an additional option for 'TexFace', which uses the alpha of the UV assigned faces as well as the colour. It appears in material buttons as a little 'A' button next to 'TexFace', when 'TexFace is switched on. It's a bit horrible, but no point tweaking that layout in isolation at this stage. This image is using texface alpha, with different assigned images, all sharing the one material: http://mke3.net/blender/devel/rendering/texface_alpha.jpg Usually I consider texface (and teaching people to use it for UV mapping) to be pretty evil, but in some cases, when you have lots of separate images that you want to control in the one material, it can be quite handy.