Sorry to butt in here but just wanted to give my opinion. First I think the winners deserve the win. The photos are great. But I think going forward allowing older pictures would change the challenge.

I enjoy the fact that I have to come up with something new each week. It pushes me to try different things and to actually get out and take pictures every week.

From my previous comment you can see the stats on not following the rules on putting mypictureday in the title. So it would be conceivable that others did not read the part about the photos being from the week of the contest.

Looking back... last week I didn't post what camera I used. So I guess we tend to read what we want to read.

As far as going forward maybe just explaining in the rules what will happen when photos are found to be old, might solve the issue. Obviously the community is going to check whether or not the content is owned by the winners. That's something most new steemian's find out quickly.

Another option for going forward is that if something like this is found after the winners are posted the winnings are split among the one or two other winners.

As examples - In this case it would go the 2nd place winner. But if it was only third place that had old photos those winnings would be split between 1st and 2nd place.

I know it takes a lot of your time to judge and review all the entries. Adding searches for other social media post would probably be unreasonable.
Again, Thank you @timsaid!