Guest Favors

Hello all of my fellow gorgeous future brides! My FH is in the Coast Guard and draws in his free time. He drew this picture of us as my birthday present a few days ago and I asked him if he would be willing to draw a picture for each family attending our wedding. He thought it would be a great idea, but now we need help figuring out how to ask our guests to send us either a family photo or a favorite picture of theirs so he has time to draw them all and have them ready to give as favors at the wedding. We want the drawings to be a surprise so we need to be creative and kind of sneaky when we ask for the photos. Any ideas on a low key way to ask that won't make them guess what we are doing would be greatly appreciated. Also, do you think it is a good idea for a favor? We want to give our guests something they would like that is more about them than us since they are all traveling for our destination wedding. Thank you for your help!