ScreenGrab to WordPress is an experimental Firefox extension that not only lets you grab screenshots of web pages but will also upload the image for you to any WordPress blog.

You can select the entire page, the entire visible area, or a custom area for the screenshot which can then be copied to the clipboard, saved as a local imaged file or can be published to WordPress as a new blog post.

This extension appears to be based on another useful extension, Screengrab, so the interface is pretty much the same.

Note that posting to WordPress requires the XML-RPC feature (WordPress 2.5+) enabled. Thanks Downloadsquad.

If you need to add annotations before uploading the image, also check out the review of DashBlog.