I just tried asking Gemini about a photo I took of my screen showing an image I edited with Nano Banana Pro... and it said "All or part of the content was generated with Google AI. SynthID detected in less than 25% of the image".

Photo-of-a-screen: https://gemini.google.com/share/ab587bdcd03e

It reported 25-50% for the image without having been through that analog hole: https://gemini.google.com/share/022e486fd6bf