Here are examples of the kind of URLs that’ll give you photos:

• A single photo:
  • /photos/schlesinger_library/13270291833
  • /photos/sdasmarchives/50567413447
• An album:
  • /photos/aljazeeraenglish/albums/72157626164453131
  • /photos/spike_yun/albums/72157677773252346
• A member’s photostream:
  • /people/blueminds/
  • /photos/obamawhitehouse/
• A group:
  • /groups/lomo/pool/
  • /groups/birdguide/
• A gallery:
  • /photos/george/galleries/72157621848008117/
  • /photos/bunnyfrogs/galleries/72157628088497125/
• A tag:
  • /photos/tags/thatch/
  • /photos/tags/auroraborealis/