For this you would use the Open Graph Tags, in this case the < og:image > and < og:description >.  These are going to be Meta tags you will place in your Large Product Layout, using the image and description tags as the Meta content. Then when the page is loaded BC will place these into the head tag of the website. 

Something like this:

<meta property="og:image" content="http://yoursitehere.com/{tag_imagepath}"/> //relative path might work, i tested a absolute path
<meta property="og:description" content="{tag_description}"/>

Another option is to use custom fields to populate these values.

This page describes the Open Graph tags you can play with:

https://developers.facebook.com/docs/opengraphprotocol/

You can also use facebook's debugger to find out what info facebook is pulling from the pages you’re looking at, so you don't have to like and unlike things.

https://developers.facebook.com/tools/debug

Hope this helps you.

Chad Smith | http://bcgurus.com/Business-Catalyst-Templates for only $7

Good looking out Liam. Thanks for the heads up.

No worries davis2121!! Glad to have helped.

Yeah, looking at your source, your image value still has your tag within it. You may check to see if the tag is correctly spelled, and if your using the large product image I don't think you can use the _value to just get the value. May be better to use the custom fields to get the path of the image.

<meta property="og:image" content="http://sweetsandtreatsboutique.2121customcontact.com/{tag_largeimagepa th}" />

<meta property="og:description" content="Our premium greaseproof cupcake liners will not fade and the colors and patterns will stay bright after baking - even with chocolate cake. No more doubling up on liners before baking!" />

The image tag is wrong if your doing it for products, your missing the _ for the path.

Also description will render the entire html for the description area not just content, HTML in a meta tag in the head? - Mess. You need to use custom field 1,2,3 or 4 as the means for your og description.

{tag_largeimage_path}

Because you uploaded with an image with captials and spaces.

Should never do this on the web as you run into many issues with files and images like this on browsers and things like this.

Files for web should ALWAYS be all lower case and no spaces and where there is a space use - or _

Files, thats why you follow the well known convention