Also, ensure if these photos are or are not shared with other users. In the case that they are, it could be that the photos are edited by another user. You can find more info about shared folders here and editing permissions here.
Even we are facing the same issue. While the phots are uploaded on dropbox there wasn't any issues with the photos but, when we download a uploaded photo from dropbox, this 'i am sorry' messege appears on the left hand side lower corner of the photo