If you had a way of projecting a pattern onto a surface you are taking a picture of, you could receive a hash, project that out onto whatever surface, take a pi

If you had a way of projecting a pattern onto a surface you are taking a picture of, you could receive a hash, project that out onto whatever surface, take a picture, and send back the signed hash of the picture you just took, thus proving that a particular picture was taken in a particular place. If that picture is of you, you can thus prove that you were in a particular place at a particular time.