What do you mean by the long side requirement of photographic works?

This is to relatively unify the format and size of photographic works.

Traditional paper can be represented by diagonal length.

However, photographic works often have many proportions, that is, the aspect ratio is 3: 2, 1: 1, 4: 3 ..., and some of them are relatively wide, and the proportions may be cut by the author himself.

In order to facilitate the printing and typesetting of future works, the length of the longest side of the works is generally limited.

Digital photos are generally defined by pixel values. Printed photos are usually in centimeters or inches.