For drawings it has to additionally be "obscene" (since obscenity isn't protected by the first amendment). And there is also a specific law that criminalizes even non-obscene realistic computer generated imagery.
Not quite. There can be more restrictions on the distribution or promotion of obscene material, but mere possession of obscene material is protected by the first Amendment: https://en.wikipedia.org/wiki/Stanley_v._Georgia
The reason why the Supreme Court upheld bans on possessing CSAM is not because it's obscene, but because it incentivizes abuse of children to produce it.
Not quite. There can be more restrictions on the distribution or promotion of obscene material, but mere possession of obscene material is protected by the first Amendment: https://en.wikipedia.org/wiki/Stanley_v._Georgia
The reason why the Supreme Court upheld bans on possessing CSAM is not because it's obscene, but because it incentivizes abuse of children to produce it.