If you like the simplicity of the Snipping Tool in Windows Vista, you will also like
FireShot, a Firefox/IE browser add-on. The cool thing about FireShot is that it allows you to edit & add annotations to an extracted image.

Steps to add a note to a extracted and cropped image -
- Install the add-on and restart Firefox
- Right click on the page to view context menu. From the FireShot option select Capture visible area and... and then choose Edit.
- The entire page opens in a new FireShot window.
- Select the desired portion of the image and click on the Crop button on the right toolbar.
- Select the Text tool in the top toolbar and click on the image where you want to write the note
Also see:
Free tools to generate screenshots