Wrong thumbnail with Like plugin

Steve,
I think your message got a little garbled some how. I think you want to be able to control the image that will display when you type your URL into Facebook. To do so, add the following tag to the page:
{JFBCGraph image=http://site.com/image-to-use.jpg}

That will set the image for the specific page it's set on. Additionally, if you'd like to set a default image for your entire site, you can add that in the Open Graph tab of the Social Configuration section of JFBConnect. In the defaults box, insert:
image=http://site.com/default-image-for-site.jpg

Once set, it will take Facebook up to 2 days to 'see' the new file. You can use the link below to check what Facebook will see though:
developers.facebook.com/tools/debug

Hope that helps,
Alex

Steve,
If the debugger is right, that's the best start you can ask for. Definitely keep an eye on it, and if it doesn't work, just send us a URL with the issue and we'll look into it further.

Thanks, and good luck,
Alex