How is photography related to physics?

First of all, electromagnetic radiation consists of electromagnetic waves, so the two terms are almost synonymous.

The very definition of "Photography" is: the creation of images by capturing radiation on a "radiation-sensitive medium". Almost always the type of "radiation" captured in photography is electromagnetic radiation, and almost always the type of electromagnetic radiation captured in photography is light, therefore almost always the type of "radiation-sensitive medium" used in photography is light-sensitive film used in cameras.

In short, photography is the art and/or science of capturing electromagnetic waves for the purpose of making pictures, except for a few rare types of photography.

Some exceptions to the standard light-with-film type of photography are: (1) infrared photography, such as used in aerial photography, since infrared electromagnetic radiation cannot be seen, unlike light, and (2) x-ray photography, since x-ray electromagnetic radiation also cannot be seen. It is conceivable that other, extremely rare types of photography such as the capturing of alpha particles or beta particles, which are other types of radiation different than electromagnetic radiation, could also be considered "photography," but those would likely be used only for limited scientific purposes rather than for recreational purposes.