I've noticed I can add a preview to an image type but it only pulls data from the settings field name in the fields within it.
Sanity.io: Get the most out of your content
Sanity.io is a platform to build websites and applications. It comes with great APIs that let you treat content like data. Give your team exactly what they need to edit and publish their content with the customizable Sanity Studio. Get real-time collaboration out of the box. Sanity.io comes with a hosted datastore for JSON documents, query languages like GROQ and GraphQL, CDNs, on-demand asset transformations, presentation agnostic rich text, plugins, and much more.
Don't compromise on developer experience. Join thousands of developers and trusted companies and power your content with Sanity.io. Free to get started, pay-as-you-go on all plans.