Web Statement of Rights is one URL, stored in XMP as xmpRights:WebStatement, that points to a page describing who owns the image and how it may be used. That page can be your own license terms, a stock agency listing or a Creative Commons deed. Google Images reads it, and it is the field that makes an image eligible for the Licensable badge.
The property comes from Adobe's XMP Rights Management namespace (http://ns.adobe.com/xap/1.0/rights/). IPTC added it to its photo metadata standard in version 2017.1 under the label Copyright Info URL, which is also what Lightroom and Photoshop show. There is no EXIF tag and no IIM dataset behind it. A program that keeps only EXIF and legacy IPTC drops it.
What Google does with it
Google's image metadata documentation says you must include Web Statement of Rights for the badge to appear, and the page it points to becomes the license link in the image viewer. Its companion, Licensor URL, adds a second link to a page where someone can buy or request a license. If the hosting page also has schema.org license markup and the two disagree, Google goes with the structured data.
The value is free text. ExifTool will store see my website without complaint, and Google then has nothing to link to. Write a full absolute URL, scheme included.
Writing and checking it
The EXIF editor has a Web Statement of Rights field for JPEG and TIFF. From the command line:
exiftool -XMP-xmpRights:WebStatement="https://example.com/license" photo.jpg
exiftool -G1 -s -XMP-xmpRights:all photo.jpg[XMP-xmpRights] WebStatement : https://example.com/licenseIn a JPEG it ends up inside the XMP packet in an APP1 segment. Pair it with a copyright notice; the guide on adding copyright to photos covers the other fields Google reads. A full metadata strip removes it, and so do upload pipelines that re-encode images, so check the published file rather than your master copy.