I do it with a MySQL datasource using the old (Grafana v6) table panel using the Sanitize HTML option. The new (v7) table panel does not have that option unfortunately but you can (at the moment) still use old (v6) table panels on v7. If you are starting with v7 I think you can alter the JSON of a v7 table panel so the type is table-old.
You just have a column which selects the necessary HTML to display your image, something like this:
CONCAT('<img src="$URLPrefix', filename, '" height="200">') as 'img' from … where …`
And then add a column style to that column and enable the Sanitize HTML option and the HTML will be rendered in the browser.