Heather, I am from a very similar Panhellenic system... two NPC orgs (we just added a local, but this will be their first formal recruitment).
From what I had heard in the past, we had done a theme party that was like a cruise where they took your picture like they do before the cruise. What we thought was a cute idea freaked out some rushees. Now, I'm a picture person, so I don't understand people who put their hand in front of their face every time they see a camera, but that's just me.
Last year our advisor tried to take pictures of the actives during the philanthropy night, but always ended up getting a PNM in the picture. Unfortunately, we feel kinda stupid using the pictures now, because every PNM she took a picture of went to the other sorority.
A group picture of PNMs might not be bad though. But keep in mind that not all of those girls will end up as your sisters, and if there's any bitter feelings between you and a girl who joins XYZ, it looks bad if you scratch out her face or put stickers over her.