There was a change to the way images are credited back in May 2019 -- see FR 1277, "Change how images are credited".
The new way works correctly on Publication pages, where ISFDB-hosted images are credited using the following line: "Cover art supplied by ISFDB on this Web page". However, the software that drives Author pages doesn't display the "on this Web page" part, which links to the ISFDB Wiki, for ISFDB-hosted images.
Anonymous
Fixed in biblio/biblio.py, installed in SVN 476 on 2019-11-30. Closing the Bug.