Flickr provides a API for searching images in flickr.We need a API key that can be obtained from yahoo by registaring a free account and agreeing the terms and conditions.Once we have yahoo account we can apply for a free flickr API key.From flickr you can download API absolutly free and use accordingly.here is one code from my drupal module that is used for getting contents from flicker using flicker API:-

<h2>Little Code part for getting search results from flicker:-</h2>
<?php