According to the manual, in Poser 6 it is possible to set an image-map node to "alpha", which means any alpha channel in the image controls whether or not the background input shows, instead of whatever the texturemap is. An obvious use would be to overlay a logo or lettering on an existing texture. The end result should be the same as using a blender math-node, with a control-map taking the place of the alpha channel. Maybe Poser expects something very specific about the alpha channel. I use an old version of Paintshop Pro, which handles the alpha channels that Poser generates without problems. And I've a vague recollection of some trickiness over just what sort of PNG file to use--colour depth or something. But I'm beginning to wonder if this is another of those things in the manual which has only a tenuous connection to reality.

ya mean like when an object has an alpha channel in its texmap, the thing behind the figure would show thru? meaning part of the figure would be invisible? I reckon it would only work with a one-sided object, as any backfaces would screw things up. as ya noted, using the blender node is the way they usually do it for lettering, tattoos or whatnot. I've also seen some of 'em recommend using the colour ramp, but that is overkill and inelegant IMVHO.

Well, I've been trying various things, and no joy. The feature appears to be in all the Poser versions of the Firefly engine, the alpha channel in the bitmap file allowing part of one bitmap to be cut out and overlaid on another bitmap. In theory. But I can't get it to work. Nothing to do with the mesh.