What a work of art is about, the subject matter, imagery and meaning, is called the ?

The answer is content as content is the one responsible of having to show what the imagery or the work of art is about. Is a way of having to express the subject matter and to depict the portrait that is being displayed as an art for viewers to see and define it in ways that they could understand.

Photography has changed its subject matter quite a lot over the past few years. in the 1800's, it was considered normal for families to have  post mortem photos of their loved ones, and now that would be completely unacceptable. i think that photographers have always pushed boundaries and have been eager to capture everything, it is just society that changes their boundaries.