WHAT? nobody even noticed my cool little torpedoes showing the logic flow directions..
Heh heh.. I purposely did not explain much more than necessary so that you braniacs would get a chance to tear my idea apart and do some thinking, in order to help me find loopholes in my idea..
Now on to the Good Question - glad you asked..
Only new valid codes would work from one contest (weekend) to the next based on dates. The code is entered before playing the mission, and then when the missions results are sent to the web site, they would be a simple data file going into your designated upload area. (It may not even be necessary to post screenshots. As a matter of fact, I highly reccomend NOT using a screenshot due to space and convienence considerations, but a patch to the game). At the end of a mission, the patch would spit out an encrypted text file any time a valid code was detected as a GAME NAME, and the encrypted file would be able to be processed by a computer rather than having a human verify each screenshot.
How does all this work?
OK, with simple encryption programs that are out there these days, (but difficult enough to figure out) any code can have the date(s) of the current 48 hour contest weekend incorporated.. no two codes would be the same, even if you couldnt see the previous date incorporated into it, and/or with large enough mixed alphanumeric permutations and compared to the corresponding number of players involved, we wouldnt run out of codes before the sun went cold quite a few billion years from now..
Now try to put your game name into Enima Rising Tide as if it were a code. See how many positions are allowed? Now multiplying exponentially each character position by the previous position and the number that represents the total letters in the alphabet, and the numbers 0-9, and just for fun, throw in some special ascii characters and you get the idea of how many times squared, times squared, times squared etc etc that are potentially usable codes..
Of course the end user usually doesnt need to worry about all this mathematical mumbo jumbo, just knowing its a really big number usually satisfies most of the curious.