Working with Schema.org documentation, found that (almost?) all images use same attribute itemprop=”image”, so why not add it to all images.
Now You can download as plugin: Itemprop WP
Here is my solution:
Script snippet: adding itemprop=”image”
On first row we add new filter to picture’s HTML output. Since we don’t care about other attributes, we simple grab must used attribute – src – and add to it itemprop=”image”.
… and search engines (Google, Yahoo, …) will love You more (because they support microdata, like schema.org)
PS. just don’t forget to correctly markup rest of code :)