add schema.org property to featured image

I would like to add schema.org information to my featured image when it is used in a single post.
I want to add the itemprop=”image” tag from the schema.org to an image in the content of the post.

The images are published when the user adds them to the post. The users are really happy with this process, they understand it, and I have just about got the rest of the product schema.org properties appearing when needed, I use custom fields for the values.

I’m sure that I need a filter to check if the image is featured when used in a single post, but don’t really know where to start.

example of a page where I need it https://www.multiliftsales.co.uk/used-toyota-4-5-ton-diesel-forklift-truck/

Thanks for any ideas