However you cut it, the bottom line is the change is effectively user account and data migration at worst.
But it would appear that in planning for this change, not all scenarios were effectively considered, and tested for success.
Even worse, across the responsible organisations, nobody has implemented a simple process to capture and address instances where the change has not worked out for the end-users. That, plus a lack of visible overall accountability where the change is concerned is pretty poor all in all.
I'm taking a wild guess the project was measured on 80/20 success, but it's not so great being in the 20%
Not limited I'm afraid to photo sites, in this case, free photo sites. The same lack of planning was recently applied to the merger of two financial investment platforms resulting in my loss of a lot of functionality.
As far as Yahoo/Flickr/Smugmug/Oath/BT are concerned I don't think anyone knows their systems and the managers aren't prepared to pay. I'd bet it's all contracted out, contract paid, contracters left, no-one caring or taking responsibility. I'm still getting rejected emails (yes I know its another topic) despite the BT mail team saying they've fixed it. It's a new world that I don't like.
I have no idea what photos I had on my BT/whatever photo site, I don't really know how to get to them. I can only say that my Yahoo email login to Flickr still works, at least for now.
Good news - Flickr/Smugmug support have fixed my account. The BT email address needs to be disassociated with the Flickr account, they will uncouple it and send you a link to associate a different email address with the account. They are now answering support requests.
There is some more information on the Flickr Help forums, the last few posts should be helpful to people:
These were originally BT accounts that BT migrated to Flickr without asking the user first. BT made the switch, so they take some responsibility for moving us to a useless (and I mean that is the truest sense) account.