You have to zoom in and actually focus on the details. Another thing is tiny breaks in the lines or multiple features merging together. It's getting better at words, but if it's a photo for example, look at the background. If the signs and text looks crisp and just more or less normal then it's fine. If background text looks generic or garbled that's means it's ai.
It is very hard and will only get harder. The next evolution is people making videos of them physically drawing as that's pretty much gonna be the only way to tell soon