Setting a limit of one image upload per participant, when you go to the "create new photo" dialog, at the botton it shows:
"You can add one more image."
And after the message it shows highlighted in orange a message box with:
"The option becomes visible when it has been approved by an administrator. This may take a while."
This is a bit misleading for the user. I think the best would be if these two message boxes are hidden in the case the limit of photos to upload is set to 1.