My friend posted me one of his photos hosted in Flickr recently, and like any hardcore photographer only provided the static link to the largest size instead of the weak-ass shrunken viewport in the default page. A typical static link would look like this (where n are numbers and a are alphanumerics):
http://farm4.static.flickr.com/nnnn/nnnnnnnnnn_aaaaaaaaaaaa.jpg
The problem with such a link is it does not expose the user who posted and owns the photo. And I did not know my friend's Flickr account. Why not just ask him? Well, I simply got curious - is it possible to trace out the user by using Flickr services alone?
Apparently, a resounding yes, very possible indeed.
In essence, Flickr provides a URL where one can append the photo's ID (nnnnnnnnnn) as a querystring parameter:
http://flickr.com/photo.gne?id=nnnnnnnnnn
It would nicely redirect to the regular photo viewer page that is starkly tied to the user account.