Take a Screen Shot Without the Shadow in Mac OS X

Instead of disabling the screen shot shadow completely you can take a one-time screen capture minus the shadow by using either the Grab app or by using the command line screencapture utility.
Using Grab is the easiest for most users since it’s wrapped in a familiar GUI. Grab is located in /Applications/Utilities, so launch that and then select “Window” from the “Capture” menu:

This will bring up the familiar window selector tool that you get when you hit Command+Shift+4, but any resulting image won’t include the window shadow.
The command line approach might be preferable to other users, so here’s the syntax you’d want to use for that:
screencapture -oi test.jpg
This too will bring up the familiar window selection tool, and any resulting screen capture will be missing the shadow.
If you want the image to go to your desktop like a normal screenshot would, use:
screencapture -oi ~/Desktop/shadowfree.jpg
You can direct the output of this command to where ever you want, just specify the proper path.
Thanks to reader inket for the Grab tip!

Shadows look better IMO, but I can see where this is useful.
[...] the available flags and what they do, and there are a variety of additional options available, like ditching the shadow, automatically launching in Preview, choosing Window Capture mode, and more. You can see a screen [...]