A trap I have discovered is that local textures do not appear to be picked up by Baked On Mesh (BOM). In the past I have used local textures when making alpha masks, incrementally tweaking the texture with GIMP on my computer and exporting it to the .tga file that the viewer is reading (this is not entirely 'safe' because the same file is being accessed by two independent applications at the same time, which can cause a crash, but it
mostly works). However if the alpha mask is being applied to a mesh body using BOM, local textures just don't get picked up at all. Even after I save the alpha and exit from the Appearance editor, the alpha appears as a blank grey surface on the avatar.
Even once I
have uploaded the alpha texture to my inventory, and applied it to the alpha on my avatar, the effect does not become visible until I have saved the change, exited from the Appearance editor, and waited for my avatar to be rebaked.
All of this makes developing alpha masks for my mesh avatar far more painful than on my legacy avatar. Why might I want to do this, you might ask? So that I can continue to wear mesh clothes that were developed before my mesh body.