PS. I'm not sure if it is just me or it is true for everybody, but I notice a substantial loss in picture quality (crispness) with 600px wide photographs, as I notice above, compared to 800px (which C-D allows without resizing). For sake of quality, IMO, it would be better if the rule was relaxed to 800px wide.
A few other changes I would recommend...
1. We can make this a weekly assignment. I don't mind taking charge if you would prefer that, with new assignment every Sunday.
2. It should be okay for pictures to be no more than a week old. That will be more inclusive of pictures some of us might have taken by coincidence. In fact, I feel that when pictures were taken shouldn't matter at all. I would rather see that the best picture there is presented, than ones taken in a hurry and generally unsatisfying to the person submitting, and not ignore some better pictures simply disqualified for being older.