Different uses. Certificate photos are mainly used for graduation certificates, resumes, etc. Generally, there are three sizes: one inch, two inches smaller and two inches smaller. 5-inch photos are generally used for daily use. The size of the photo is in inches, and 1 inch is equal to 2.54cm. Usually, x inch refers to the inch length of the long side of the photo. For example, 5 inches means that the photo length is 2.54×5, which is equal to 12.7cm.