For .jpg image files, I can add text notes to them very easily: in
IrfanView, I just (open the image and then) type I (info) then C
(comment).

This doesn't work for the .png file format.

_Does_ the .png format _have_ a metadata text field? If so, what utility
lets you see it, and ideally edit it?

(I'm talking about text that _becomes part of the file_, not that is
attached to it in some "album" type management system: such that it
remains part of the file even if the file is renamed, moved, or even
emailed.)
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Science isn't about being right every time, or even most of the time. It is
about being more right over time and fixing what it got wrong.
- Scott Adams, 2015-2-2