Need magento expert to do some coding with addthis image button

I Have a magento website http://safetbox.co.uk
when you are at a product page you will see the addthis social media sharing button above the SKU. The problem is that when users want to share the product on facebook it will display everything except the correct image.

example= http://safetybox.co.uk/20-person-first-aid-dispenser.html

the addthis button has been installed through magento connect and with modification i have managed to display it on each product page, however after many failures i cannot get the right image to display so i need help (probrably a simple line of coding)so expert in magento only please apply.

questions? please ask me

regards
dean