Finding PNG Images Larger Than x Pixels Through the Linux Shell

When you are trying to work on changing the design of your website, you have to be concerned with the width of the pictures in your article content. I've got notoriously large screenshots on most of the articles I've written, so if I want to increase the sidebar it's critical to figure out which pictures are going to be too wide to fit in the new design.

Since I'm a programmer, it would be easy for me to write a small application to do this, but it made me start thinking… why can't I do this on the Linux command line?