EXIF should be fine.  I always use an image taken during the challenge period or if I don't get one I have no entry.  That is quite fair and timelines are one reason this is actually a challenge to me, besides producing a  photo good enough to enter.

Michael, I can understand you concern for the beginner and feeling of advantage to the more experienced.  I was pretty new at digital imaging when first entering a challenge, am better now but still far behind the really great photographers here. I grew by seeing the photos by others in both techinical and artistic levels. And, I cannot remember a challenge in which many really poor images have been entered. The choices are generally not easy when voting.
I cannot agree that the most postworked will "please the eye" better than the quite well composed photo with minor postwork.  The winning entris are certainly some or experience but also of personal point of view and creative thought of the challenge theme.

I would not vote for a poor photo any more than vote for one appearing over postworked.  Seeing the creative photos of others is a benefit of the challenge area and as in other contests. What the viewers select as best to them will be,  even if that disadvantages the raw beginner. I see no reasonable way to level that playing field and am not certain such would be desirable.

My real wish is more entries but more than that more voters.

Your thoughts are appreciated.        Tom.