SEAL is based on the publicly reviewed and widely adopted DKIM for securing email. There are few independent reviews of C2PA, and they are all negative -- C2PA does not provide validation. (My own blog repeatedly demonstrates weaknesses in the C2PA solution.)
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https://spectrum.ieee.org/meta-ai-watermarks Article says Meta's AI Watermarking, but talks about C2PA's approach. "Flimsy, at best".
https://www.technologyreview.com/2023/07/31/1076965/ MIT Tech review says C2PA will "not stem the harm of machine-generated misinformation."
https://hackaday.com/2023/11/30/falsified-photos-fooling-adobes-cryptographically-signed-metadata/. Hackaday describes how to use Adobe's C2PA solution to create authenticated forgeries.
https://hackerfactor.com/blog/index.php?/archives/919-Closed-Standards.html