@frugally4u - Thanks for trying to help, really appreciate it! I checked the links but they're for other themes and the files/code mentioned in them aren't the same as in Shoutbox :(
@rumblefish - That is true, but then readers can't click the thumbnail to get the single post page either.
For now I've removed the hover/magnifying glass effect, so at least people aren't prompted to click.
I'm using a large image for the single posts and the lightbox actually shows the image in a smaller size than on the page, so that's why I want to remove the lightbox from single posts. Here's the a single post, if you're curious: http://worlddailyphoto.com/india/magnificent-taj-mahal