A security feature implemented by Facebook in May requires some users to identify friends from photos in order to log in from an unfamiliar computer - tough for a bot or an imposter to fake. But it's also a major annoyance for some who have been denied access to their accounts after failing to correctly identify photos of dogs, objects and acquaintances they don't know well enough to recognize.

Facebook has already added a question to its FAQ specific to the issue: "I can't access my account because I don't recognize anyone in the photo security check."

Facebook user Eleanor Herman was directed to the security check after trying to login from a laptop computer at the beach instead of the one she normally uses. She's an author who is 'friends' with her readers, many of whom she does not know personally, and she has not been able to correctly identify the five out of seven photos required to access her account. Facebook makes her wait an hour before attempting the security check again. She said she has been unable to access her account for 10 days, and sent us this screenshot:

It's easy to see why this test is difficult for many Facebook users to pass, and difficult to understand how Facebook failed to realize this.

Facebook encourages us to 'connect' with as many people as possible, however marginal the relationship, so it's not surprising that users can't recognize every face in their growing 'friend' banks. Users upload and tag pictures of animals, food, objects, landscapes, abstract art and groups of people jammed together - the volume of photos mistagged as inside jokes is enough to invalidate this as a way to verify a user's identity.

Facebook says it is relying on tagged pictures from friends with whom a user is likely to have a close connection, similar to the algorithm used to decide what to display in a user's News Feed. But users are understandably getting frustrated:

UPDATE: Facebook responded to say only a small percentage of users have any problem with the photo security check. It's found the method to be more effective than other kinds of security checks, a spokesman said, and Facebook is always working to improve its systems.