Picture doesn't mean photograph. The word picture predates the invention of the camera. That's why the word photograph was created in the first place, to differentiate it from other types of pictures. A photo is what comes from a camera, a picture basically means any kind of image. An image of JUST text probably doesn't qualify as a picture, but pretty much every other image does.
If a person wants to just see photographs then I'm sure there are plenty of c/photos communities for that.
But with that said, this community isn't c/memes or c/socialposts either, so a nuanced bit of a moderation hand could certainly be warranted.
And with that also said, moderators can do whatever they want with their own communities. So if you wanted to limit it to like just text posts instead of any pics then that would be up to you to decide too
https://dictionary.cambridge.org/us/dictionary/english/picture