Guestbooks are a common sight at a Wedding Reception where guests can leave notes for the happy couple. An alternative to having a traditional guestbook is to use an instant camera.
My preference of instant camera is the Fuji Instax 210 Wide.
The Fuji Instax 210 Wide is a camera, much like an old Polaroid, which produces instant prints on 3.4" x 4.3" film. The actual image measures a little smaller at 2.4" x 3.9", this leaves a small white border at the bottom of the print.
This white space can be used by guests to write a short note using marker pen. I find that Sharpie Fine Permanent Markers work best as they do not smudge. Alternatively you can mount the whole print in a scrapbook and write a message on the scrapbook page itself. If you choose the scrapbook option, you will also need Photo Corners to mount the Instax prints to the pages.