Facebook, you make me want to cry!
It seems that the way in which facebook chooses an image to show alongside a posted link differs for links posted in different ways.
Oh how fucking hilarious. Not.
On our product page if you "attach" the link, or share it using facebook sharer (http://www.facebook.com/sharer.php) it picks the big product image as the first image in the list for you to choose from. This is a Good Thing, and exactly what we want to achieve.
However if you click the like button, its picking up a random image from sets of smaller images elsewhere on the page.
e.g. Share this dress' page through the sharer, or by "attaching" and you see this image:
but if you use the like button it shows us this image,
which is for this dress.
Arrgghh that's annoying. Get a damn grip facebook, at the very least you could try to be consistent. Read about the principle of least surprise.