Today must have been my lucky day....after turning off all antivirus/spyware/pop-up/phishing blocker I had, I tried yet again to log on and lo and behold....there the missing photos were!
I had tried this very same method at least 3 times in the last week, but it never worked. After the photos were back, I then systematically turned on every option I'd just turned off...each time checking to see when the photos would disappear so I could identify the offending program/block, yet the photos never went away. Well beggars can't be choosers, I suppose!
Things are fine on Firefox and Opera as well.
So thank you to all who helped try to unravel this mystery with me (especially you, Broni!)