From https://exiftool.org/TagNames/EXIF.html…
See the / after the word string? That means “avoid”.
Hugo uses rwcarlsen/goexif to read EXIF data, and it can’t read the Title.
ImageDescription works fine, as does ImageUniqueID, but I would reserve the latter for a unique identifier (e.g., the signature generated by ImageMagick’s identify -verbose -format %# a.jpg).
You could also hijack Artist, Make, Model, or Software. Some site authors use the file name to generate the alt attribute; I suppose you could do the same with title.