Nope, there's no way to tell Facebook not to use certain images. However, you can use the Open Graph section of JFBConnect to have it pull the first image in an article or K2 text to use. Additionally, on any page you want to specifically set the image, you can add the following code:
{JFBCGraph image=http://site.com/image-for-page.jpg}And, finally, you can set a default image (like a logo) for your whole site in the JFBConnect Open Graph config area by putting in:
image=http://site.com/default.jpg
This last piece is good for any pages that aren't content and that you haven't set a {JFBCGraph } tag on.
Hope that helps, but if you need more info, just let us know!
Alex