I can get collections by method flickr.collections.getTree. 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.
Otherwise url contain some default url: \images\collection_default_l.gif.
But what's the full default url?
My bad. Solution is simple, should add only flickr.com:
