The word "automatically" is always scary. Because I'm a pretty heavy user of metadata, I'd want a list of all possible metadata from which I could choose all the fields I need, and the ability to set up import template(s) so I don't have to choose each time. At a minimum I'd want title, description, author, date taken, rights, tags, comments. And the option to include any data about camera/lens/exposure/GPS/etc. that seems useful, which would vary depending on the image's origin and purpose.
Here's an image that has most of the fields I'd want (download link is below the image):
(I don't know if the one shown here still has its metadata, but the linked one should.)
I could also export an .xmp file from Photoshop if that would be useful.
Or you can see a lot of the EXIF data here: https://flic.kr/p/LGU2n8
It's unfortunate that not all file types allow tagging/metadata. I've been getting images of portions of newspaper pages from Chronicling America (by zooming in to what I want and then right-clicking and saving image--more efficient than downloading a PDF or JP2 of the whole page and cropping it), but they're PNG files. Can't be tagged, so I guess I'll have to batch convert to JPG if I want to work with their metadata (or want Tropy to eventually be able to write metadata to them).