What is Flickr? I think you landed on this page because you know what Flickr is, so let’s come to the point and discuss about the API. Why am explaining? Although each and everything, about API, is well documented on Flickr website here , I'm just trying to explain the whole process by dividing it into small parts. Old Authentication API The current Flickr authorization scheme is not the first one it used. In the early days of Flickr, users granted the power to an app to act on their behalf by giving the apps their Flickr username and password. Doing so meant that in order to revoke an app’s permission, users would have to change their Flickr password. Of course, doing that would also instantly revoke permissions of other third-party apps with knowledge of the user’s password. The new authorization scheme is meant to correct obvious problems with the old scheme. Why should you as a user have to use your Flickr password for anything other than your dealings with Flickr?