The best way to stick photos in a scrapbook depends on what is most comfortable for you to use, the materials being stuck together, and the size of the materials.  Glue dots are great for smaller materials, a glue pen is easy to use, and liquid glue is best for embellishments like plastic or metal adornments.  Some glues might not be age-appropriate; for example, a hot glue gun might be inappropriate for small children who could burn themselves.