Not applescript
No, not applescript.
Just press Command + Shift + 4 keys at the same time and the cursor will turn into a cross-hair.
You can then draw a box around a portion of the screen and it will save that image to your desktop as a .png file.
Additionally, after pressing Command + Shift + 4 and getting the cross-hair, you can press the space bar once and the pointer will turn into a camera.
In this mode, it will take a screenshot of whatever window you hover the pointer over and click.
Hope this helps.
Cheers,
Mark