Two weeks ago I ran 100 images through four AI image detectors to pick the engine behind a small checker I built. Since then OpenAI shipped GPT Image 2.5 (September 8) and Google shipped Nano Banana 2.1 (October 6). A detector that was fine on last season's models can fall behind quickly, so I retested the checker as it actually runs today on the newest generators I could get clean samples from.

The question was narrow: how often does an image from a new generator come back as anything other than "Likely AI-generated", and how often is a real camera photo flagged?

Rules first, results second

I wrote the protocol down before the first detection call: which images, how they're picked, how answers are counted, and what I'd change on the site depending on the result.…