How can I watermark images with a taxonomy term from the node they belong to?
Problem solved — Rainer Feike's comment prompted me to examine the field setup and I realized I had made an error in the way I set it up that was causing the token not to resolve (there were two taxonomy fields on the original product content type, referencing two different vocabularies, and I had matched the wrong field name with the vocabulary in setting up the test content type I was trying out the new image style on).
Once I corrected that it worked. My apologies for posting about what turned out to be a self-created problem.