How can I retrieve individual photo's through the API? And on what basis can I do this? Do I need to store the URL, or some kind of ID?
You can use PeopleGetPublicPhotos, or do a normal PhotosSearch and set the UserID. I'm not sure what you mean about storing the URL?
Users can insert filckr URL's to augment metadata with flickr photos. I want to retrieve the flickr metadata based on this url.
I found the solution: through PhotosGetInfo, based on the photoid that I can extract from the URL.