Poser 7 (and up) can stubbornly cling to a texture file.  It has some kind of internal
database of textures, and will use its "familiar" texture instead of the new one.

Try saving the altered item as a PP2; then edit the PP2 file and be sure every reference
to the JPG is the new one.  (There will typically be two mentions of the JPG for each material,
once in the "old" material list and once in the ImageMap node.)

Restart Poser and load the prop.

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