We did the same in France, leaving a message in the middle of the competition saying that there's no limit. We've seen some users adding new pictures after that (but without knowing if it was because of the message).

2013/11/20 Federico Leva (Nemo) <nemowiki@gmail.com>
As suggested by someone, I also thanked all those who had uploaded only 1 or 2-3 images to WLM-IT, reminding them there were no limits. I don't know if others followed that suggestion though.