Define easily. There is an approach that apparently works and is based on spectral analysis of the images.
https://github.com/aloshdenny/reverse-SynthID
FWIW there are a few people in the issues saying that the tool is giving false negatives and the output image gets flagged by the actual Gemini API as having SynthID. Most recently 3 weeks ago without a response.
alt Hacker News
FWIW there are a few people in the issues saying that the tool is giving false negatives and the output image gets flagged by the actual Gemini API as having SynthID. Most recently 3 weeks ago without a response.