I've seen many artists just do it for all of them but if you only want to do one then I'd recommend looking at who's note with screenshot of it came in to you first about it as that probably means they were the real winner.
I was actually meaning the notes they sent you, who ever got their note in to you first would be the winner most likely.
As for their screen shots, the times at the bottom of their screen grabs might not have helped you anyway if you consider time zones and they may have all been in different ones... But now as I'm thinking about it you'd probably go on the minutes rather than the hour. Either way hope it gets figured out.
I like the 4 headshots idea... since they all caught it, and will be very excited to have done so... I know I'd be bummed if I sincerely thought I had caught it only to realize that I wasn't the only one XD