I have recently tried entering an online photography competition only to find that if I am successful they will need an original image but one that is not DNG. They say that this is because they can not prove if a DNG has been edited. Is there a way to prove that it has not been edited, are they missing something? Or am I simply up the creak without a paddle.
If you are talking about Lightroom (are you?) there's really no such thing as an edited DNG, the pixels in the image portion of the file remain as they were when they were captured by the camera. LR can add edits to the file as text, these are easy to identify, and the original pixels are still there unchanged.
But if they believe that a DNG can be edited, then so can any other original image. You can go into any file with a binary editor and change any piece of information you want, if you choose to do so.
You are not up a creek without a paddle, you are dealing with people who aren't making any sense.