We use a handy little app called LittleSnapper to annotate screenshots. LittleSnapper lets you easily capture web pages, screen shots, jpgs, or even DOM elements (portions of a web page, like a table or paragraph). Once you’ve snapped something, you can add notes, arrows, lines, boxes, circles and more to the image.

We’ve found this to be great for things like marking up design comps with notes (for clients or for the designer) and leaving notes for a developer so she knows how something should be coded. For even more ideas, check out the LittleSnapper case studies.

Once you’ve annotated an image, it can be exported as a jpg/png image or you can share it on Flickr, Quicksnapper (LittleSnapper’s sharing service), or FTP/SFTP. There’s also a companion app for the iPhone.

If you need to annotate screen shots, LittleSnapper is definitely worth a look.