With BOSS at least, requirements for displaying image results (which I believe only pull from public sources - I could be wrong there) are quite strict. See http://developer.yahoo.com/search/boss/bos...ge_Queries.html for specific information on that. I believe any users not doing so would be in violation of the terms and services, but it's best to check with the search teams directly for this info. BOSS image results state that:
Requirements: You must 1.display the title or abstract of the image when presented in the search results; 2.display at least the first 40 characters of the referurl field which indicates the source page; 3. for the source page referurl, use the unmodified referclickurl field to navigate to the respective source page; 4. If the image is made clickable, either use unmodified refereclickurl (to the source HTML page) or clickurl (to the image) for the navigation link.
It looks like Evan Goer also responded to your BOSS group posting - I would use his suggestion as the "official" perspective from Yahoo! since copyright issues with automated search results are tricky.