Aha -- some progress.
Opera's privacy error page had the term
NET::ERR_CERT_COMMON_NAME_INVALID
displayed (for what it's worth).
Anyway, next I took FreddyBob's advice and tried loading UKLDF thru a VPN.
It's just a bit slower, but that did the trick! I could view all the photos again.
So, I still don't know what the hangup with
ibb.co is, but at least there's a workaround.