Comments are not the same thing as captions.

A caption is a description, and should be an explanation of the image, its context, its story, and so forth, most often written by the photographer - while a comment is a reaction to the image, often written by somebody else. The caption is what a museum would place next to the image if on display; comments are what museum visitors would leave in the guestbook after seeing the image.

Captions typically have a factual tone; comments are opinions. Captions may be used by the photographer to provide accessible alternative text for visually impaired users; comments express the personal thoughts of the commentator.

Digikam should support comments as a separate type of metadata. The value of comments comes from their multiplicity - an image may receive many comments, over time.

For example, I might tag and caption a photo and then add a comment saying "Yeesh I look so embarrassing in that hat.". But then ten years later, I might return to the image and add a further comment: "How times have changed now that hats are back. This is now one of my favourite selfies."

Comments do not overwrite previous comments; they accumulate over time.

Comments should have an Author and a Timestamp.

Comments should be written to XMP sidecar files alongside other metadata, in the digikam namespace if there is no more standardised way of expressing them.