Selecting the thumbnail that is shown when posting links on Facebook


I'm not sure if this is possible, but thought I'd ask! When posting links to product pages on Facebook, the thumbnail image that shows up is very rarely the product image itself. Is there any way to specify that the main product image is the one that is displayed when sharing a link to a product page?

I am thinking it is perhaps possible with the use of an image source meta tag but not sure how to get it to choose the main product image.

Any pointers would be much appreciated!

Thank you