title: Get defaut collection image by Flickr API
body: <p>I can get collections by method <a href="https://www.flickr.com/services/api/flickr.collections.getTree.html" rel="nofollow">flickr.collections.getTree</a>. Each collection have large and small url image. If collection have mosaic image, then url is full url like https:\farm2.staticflickr.com\xxxx/cols/yyy_zzz_l.jpg.</p>
  
  <p>Otherwise url contain some default url: \images\collection_default_l.gif.</p>
  
  <p>But what's the full default url?</p>