If I go to an article on your page, I do not see an Open Graph Image tag defined. An example is
here
. If you run this page through the
Facebook Open Graph Debugger
it states that
1) an image tag cannot be found
2) when Facebook attempted to pick a best image, the one it picked was not big enough (hence the blurry)
There are several different ways that you can resolve this, but I think the easiest would be to turn on our 'Open Graph - K2' plugin. Then go into JFBConnect > Open Graph > Objects section and create an object for your K2 articles. From there you can set the og:image tag up to use the appropriate K2 image. After you set this up, you will need to go back into the Debugger and re-scrape the page to make Facebook recognize the changes immediately.
Try this and let us know if you need further help.
-Melissa