Different photo sizes due to the different types of photos that are used for different purposes, such as small prints to go into an album, to larger prints to display on walls. The right size may be based on the content of the image, display space and the purpose for which it is intended, according to Visuals Clipping. The smaller sizes like 4x6 are great for use in albums, and the larger sizes can help to make portraits and artwork stand out. These factors should be taken into account prior to printing so that the photograph will fit the frame and space it will occupy.
Read more- https://www.visualsclipping.com/blog/standard-photo-sizes/