So then I decided to create a new Flickr-actually-Yahoo! account. Being the genius that I am, I used my main Gmail address for this. When I tried to log in, it told me, "We noticed that your Yahoo! email address ([Edit: the email used to sign up]) is already registered in the Flickr database." It gave me two options: merge my two accounts, or "continue to explore Flickr." What they do not mention is that if you choose the second link, you are redirected to a different page and are not logged in. This, of course, causes one to return to the login page, which, obviously, sends you right on back to the "merge" page.
The first option, merging accounts, requires one to log in to the other account with the email one used for Flickr and the password, of course. The original problem reappeared! I ran through all the passwords I could ever remember using, but to no avail. This time, the Flickr-only password retrieval was easy to find, but when I put my email in, it told me that it is associated with a Yahoo account, and therefore, I cannot get the password.
Therefore, I cannot log in. In consequence, I cannot merge accounts. As a result, I cannot log in period. Do we see the problem here?