Sounds like a good idea, if you also receive a freshly made hash: to ensure the picture was taken _after_ the received hash and _before_ it was sent out. I wou

Sounds like a good idea, if you also receive a freshly made hash: to ensure the picture was taken _after_ the received hash and _before_ it was sent out. I would make a merkle-tree-like hash to be able to obscure parts of the picture and still be able to prove the date.