*The use of poster board or foam board is up to you. If you will be using actual photographs instead of photocopies then I would recommend that you use foam board, because it is sturdier. However, if you will be making photocopies of your photographs then the poster board should be fine. The price difference between poster board and foam board can be anywhere from $3 to $5, so price may be the deciding factor. If this is a project for kids to do, poster board should be fine.
Your next decision will be to use the actual photos in your collection, or to make photocopies. If you have doubles of your family pictures then you can use the second set of prints for your collage, or if you have digital photographs you can print out the photos that you want to use. If you don't have a digital camera, or if you don't have double prints available, you can also scan your original photographs into your computer and print out copies to use in your photo-montage. While scanning and printing may take more time than the other available options, it does allow you to alter the size, shape, and content of the photographs, which will allow you to customize your montage even more.
Once your usable prints are ready, and you know how you want to layout your montage you can start gluing your photos to your board. A glue stick, rubber cement, or spray adhesive will work best for this type of project as they won't curl your paper, or leave ripple marks on your prints. As you progress through the gluing stage, every now and then step back and examine how the montage is coming together. This look from a distance will help you to gage how others will be seeing it when it is hanging on your wall, and you will be able to better determine if it seems balanced and well coordinated.
After all of your prints have been secured allow your photo-montage to dry at least overnight. Even though the glue might dry faster than this, with several layers of prints it will take longer for the glue to really cure and set. The next day check for any loose prints or corners that need to be re-secured. It is important to make sure that all the outside edges of your montage are secured. This will reduce the chances that a print will be damaged or pried loose because of moving, drafts, or breezes. When you are sure that the montage has dried you are then ready to display your piece of art. If you have the money available you can mount and frame your art, however, if framing is not in your art budget you can use double-sided tape, push pins, or thumb tacks to hang your photo-montage.