This would mean using fileinfotpl_art_title as a fallback for fileinfotpl_desc. I looked into doing the fallback directly in the template, but because we're using IDs, that can't work.

(In reply to Maarten Dammers from comment #0)

Both Artwork and Book require either description or title to be set. Now
artworks and books that only have the title set (and not description)
incorrectly end up in
https://commons.wikimedia.org/wiki/Category:Files_with_no_machine-
readable_description

I would argue that's correct, at least in theory. A title and a description are different things (and will have different fields in the structured data); having a title is no reason not to add a description as well. For one thing, key concepts should be wikilinked in the description, which practically never happens in the artwork/book titles. Also, the titles are messy - e.g. half the HABS ([[c:Category:Files_from_the_Historic_American_Buildings_Survey]]) images have a "title" which is the concatenation of the actual title and the description; for other files it is a concatenation of the actual title and the source. So there is no reason to exclude these files from a description cleanup drive, IMO. For the same reasons, I don't think it makes sense for the template to pretend its title field to be a description.

In practice, we might want to say such images are less problematic than ones with neither title nor description and the category should be limited to those, at least initially; I'll defer to you and Guillaume on that.

https://commons.wikimedia.org/wiki/Category:Files_with_no_machine-readable_description got flooded with over 260.000 files. I disabled the category for now pending a fix.

Currently CommonsMetadata does not make any distinction between the title field of the template and the EXIF title; and the EXIF title tends to be crap.