add thumbnail to an offering

Summary:

How can we add thumbnails or images to an offering to show if this is self-paced or instructor-led for example?

Content (required):

We're adding thumbnails at the course level, but I've seen some examples with an image at the offering or activity level. How can we do create those images?

Version (include the version you are using, if applicable):

21C

Code Snippet (add any code snippets that support your topic, if applicable):