It would definitely need to be subscribers only as others can't post images anyway.
An issue that's missing is that ideally this is not a repeat of other Forums yearly offerings instead a more frequent offering. As such it shouldn't be just about individual images rather in some cases sets/series etc.even profiles, in the way that APUG once had a monthly Profile feature.
and i think that someone OUTSIDE of apug needs to be the judge+jury
membership is too close to the work in the gallery ...