Combine the couple's wedding invitation and a photo from the ceremony or an engagement photo with an old, hardcover book for a gift they will show off for years to come. Start with a book that has pages slightly larger than the invitation and photo you would like to use. Make sure that the cover and binding are in good repair, and that there are no obvious tears in the pages. If you can find an old romance novel, even better.
Open the book to the center so that it will lie flat while open. Combine three parts white glue and one part water. Use a small, foam paintbrush to paint the mixture onto the edges of the pages. Allow the mixture, which is similar to decoupage medium, to dry for about 24 hours. It will harden as it dries, holding the pages together.
If the pages are not firm enough when dry, apply a second and even third coat, allowing them to dry between applications. Placing one or two other heavy books atop the open pages while drying will help compact the pages, and you can wrap the book cover in plastic wrap if you are concerned about the glue mixture dripping onto it.
Once the pages are dry, use a glue stick to adhere the wedding invitation to one of the center pages and the photo to the other. You may want to make copies of the photo and invite first so that you can modify them, making them similar in size. Apply the glue and water mixture around the edges of the invitation and photo so that they will stay attached to the book. Place in a large box filled with tissue paper before wrapping.