Yes, color checker should be fine and it’s absolutelly 100% CC0 since YOU made the photo, not the checker
Just gotta make sure it’s well exposed, no black data along the edges etc.
Maybe some of that would be ok, but I do believe that the text excerpt there should be fine.
As for smartphones & action cams - as long as they can produce RAW files natively i think those might be uploaded. However most of those should be DNGs and therefore should “just work” ™ ![]()
That would IMO create unnecessary overhead for RPU maintainers so no, exif data should be enough.