One can want Exif, XMP, IPTC or DC, RDF etc. The problem I see here is that none of them are standard in PNG. Thus, one cannot be sure that all softwares can read (and more important, save after edits) the metadata.
A first simple step would be to use the iTXt chunk, with standards keywords. Then, as the specs permits to add new keywords, it should be possible to support XMP or a subpart of Exif as well (as far as I comprehend the specs, but I'm not an expert).
One can want Exif, XMP, IPTC or DC, RDF etc. The problem I see here is that none of them are standard in PNG. Thus, one cannot be sure that all softwares can read (and more important, save after edits) the metadata.
A first simple step would be to use the iTXt chunk, with standards keywords. Then, as the specs permits to add new keywords, it should be possible to support XMP or a subpart of Exif as well (as far as I comprehend the specs, but I'm not an expert).
More infos: libpng. nigilist. ru/pub/ png/spec/ 1.2/PNG- Chunks. html#C. Anc-text heim.ifi. uio.no/ ~gisle/ blog/?p= 3
* Some details on the keywords: http://
* Some links about PNG and metadata: http://