Glacial Potholes

 

 A photo of some glacial potholes to claim a find for an Earth Cache

  

Some geocaches (like virtual caches and earth caches) have no logbook to prove that you found it, so a common means of proof is to provide a piece of information that you would only be able to get if you visited the spot, or a photo with your GPS in it and post it in your log or email it to the cache owner.