OpenAI now tries to hide that ChatGPT was trained on copyrighted books, including J.K. Rowling's Harry Potter series::A new research paper laid out ways in which AI developers should try and avoid showing LLMs have been trained on copyrighted material.
It’s a complicated answer I’m unqualified to answer but essentially there exists some sort of baseline either for people or for how gpt responds usually and then they can figure out which way the text “leans”
“Existing detection methods can be roughly grouped into two categories: black-box detection and white-box detection, black-box detection methods are limited to API-level access to LLMs. They rely on collecting text samples from human and machine sources, respectively, to train a classification model that can be used to discriminate between LLM- and human-generated texts. An alternative is white-box detection, in this scenario, the detector has full access to the LLMs and can control the model’s generation behavior for traceability purposes. In practice, black-box detectors are commonly constructed by external entities, whereas white-box detection is generally carried out by LLM developers.”