*Offer a frame that everyone can sign, and use it as a meaningful frame for a wedding picture or two.
*Some brides and grooms rent photo booths and ask guests to affix instant photographs of themselves on blank pages in a book, accompanied by written messages. This could be possible, if I'm able to barter with the photo booth company with which I've been speaking!
*One of the rare men who responded to my wedding posts (lol) suggested putting out a book of photographs of the bride and groom together. At his wedding and reception, he also gave guests themes, such as "What's the key to a successful marriage?", to encourage guests to write more than their names.
*Ask guests when they RSVP to send you photographs of themselves, then use them to create a scrapbook and ask guests on The Big Day to sign alongside their photographs. Not only do you receive messages, but you have a built-in reminder of what people looked like at the time.