Use's OSX's screencapture to capture an area of the screen, save it to a temporary file, and pass it to LaunchBar for further SendTo processing. The bundled actions don't do the second part.
The image is optimized via ImageAlpha's pngquant. Hold down alt and it will also use ImageOptim for best results.
A few actions that may go hand-in-hand with this one:
Note: press space while selecting the screenshot area and you can select a whole window to capture!
- Optimization inspired by pregnagha's Screenshot action