Re: Embedding C2PA metadata in PNG

When we started on v3, @Chris Lilley<mailto:chris@w3.org> asked me if I wanted to include the C2PA’s tag in the PNG spec, and I told him that I didn’t see the need.  However, if the PNG committee would like to bring it into a future edition, I am not objectionable as I consider it frozen at this time and would welcome the “back pointer” from PNG to our work.

I am happy to write the (most likely very short) paragraph for PNG v4 on the subject.

Leonard
Chair, C2PA Technical Working Group

From: Chris Blume (ProgramMax) <programmax@gmail.com>
Date: Friday, August 22, 2025 at 4:45 AM
To: Fares Alhassen <falhassen@google.com>
Cc: Portable Network Graphics (PNG) Working Group <public-png@w3.org>
Subject: Re: Embedding C2PA metadata in PNG


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We haven't considered this as a group. This is the first I've heard of it.
I like the idea. Although, maybe it should be a topic for PNG 5e instead of 4e.

We're quite behind schedule on 4e. A lot of this is simply because we're blocked waiting on other specs. We're supposed to have a First Public Working Draft soon.
Since we're blocked, we could perhaps amend the 4e plans to include it. But if there isn't pressure to include it quickly, I personally would prefer to add it to 5e. I'm open to the group's thoughts here.

On Fri, Aug 22, 2025 at 12:49 AM Fares Alhassen <falhassen@google.com<mailto:falhassen@google.com>> wrote:
Dear all,

The C2PA specification has a private caBX tag for C2PA metadata (which is encoded in a JUMBF box): https://spec.c2pa.org/specifications/specifications/2.2/specs/C2PA_Specification.html#_special_consideration_for_png


I was wondering if the W3C PNG group has considered making C2PA a part of PNG 4e as well and working with the C2PA organization to graduate it to an officially supported feature of PNG. I'm happy to talk about it in our next meeting (along with the gainmap discussion).

Sincerely,
Fares