Find Images by Exact Dimensions

Everyone knows that Google Image Search sports a drop-down menu for filtering results by small, medium, large, and extra large sizes, but if you're looking for the perfect wallpaper, for example, the imagesize operator is even better.
Weblog Design Live uncovers the undocumented search operator (that's also new to us) and demonstrates how to use it.
Just use the imagesize operator followed by the WidthXHeight in pixels, like so:
Here's an example:

[imagesize:640x480 muffin] finds 640px x 480px images related to muffins.

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