Glad to hear JFBConnect is working well for you. To get the image from a K2 article properly when the Like button is clicked, please install the Open Graph - K2 plugin that's a part of the zip you downloaded here. Once enabled, that will try to select the best image for the article. There are ways to have more control of the selection, but I'd just start there
Once enabled, you may need to have Facebook re-scan a page to test using their debug tool below:
developers.facebook.com/tools/debug
After you scan the page, it should work. Facebook will re-scan all of your pages over a 2-3 day period as well.
Best of luck,
Alex