I love that photo frame idea! sounds wonderful. I actually didn't have bridesmaids, my wedding party was all guys (i have 3 brothers and i had a small wedding). Anyways, i think the frame idea is great. Maybe you can meet your girls for lunch and have the frames come out with dessert or something so you are there to see their faces. Or have some kind of invitation come to the table by the waitor, maybe something like "Ladies, i have just received an important invitation for you!" Well, something along those lines.
Wish i could be more help. I actually, wished, i had thought of that. I would have done something special too. Oh well, maybe i could do a commerative photo frame like that and mail it to them as a thank you for being a part of the wedding? That is such a great idea, and not that expensive. But, even though not too expensive, very precious and memorable.
Good Luck to you, Can't wait to hear what you do with this. Such a marvelous idea ladies, something special as an invite. So jealous now that i didn't think of it...LOL.
Have A Magical Day!!