OAuth (Open Authorization, http://en.wikipedia.org/wiki/OAuth) is used by Flickr when user authorisation is required. For example when an application is trying to access user's private photos. OAuth is decribed in http://oauth.net/core/1.0a/. The use of OAuth with Flickr is described in http://www.flickr.com/services/api/auth.oauth.html.
For many programming languages ready-to-use implementations are available (http://www.flickr.com/services/api/). Here I show how to implement Flickr API OAuth authentication in Matlab.
This tutorial can be also used by developers in other languages since Matlab is very easy to read, and I concentrate on Flickr requirements to OAuth implementation rather than on specific programming techniques.
The Flickr explanation of the process is rather hard to understand. Besides in lacks some important details. This work could not succeed without helpful hints from Sam Judson on http://www.flickr.com/groups/api/discuss/.