Google has now added the still in BETA image license structured data markup to both Google Search Console's enhancement reports and to the Rich Results test tool. So now if you use this image license markup, you can debug it in both of those toolsets.
Here is Google's announcement:
We are happy to announce 📢 support for Image License structured data 📸 in Search Console in addition to the Rich Results Test tool. Read more about Image License at https://t.co/aqMap8bEby and about the Search Console report at https://t.co/8pVYPCW6Oy pic.twitter.com/rJ8Huh33Kp
— Google Webmasters (@googlewmc) July 30, 2020
When you add this metadata and when Google decides to show the results in image search, Google may show a new Licensable badge for the image. If Google does not add the licensable badge then you may want to debug it with these tools.
Here is what the badge looks like:
Note, if you do not see the "image licenses" option under the enhancements section in Search Console - then Google does not detect the markup on your site at all. Here is what it would look like:
And/Or you can run it through the Rich Results test tool for debugging your pages in real time.
Forum discussion at Twitter.