While Selenium has built-in support for capturing whole page screenshots, usually screenshots must be cropped and some times also annotated to make them useful in a documentation.
A Robot Framework library called Selenium2Screenshots provides a collection of re-usable keywords for cropping and annotating screenshots.
A cropped and annotated screenshot could look like this:
*** Settings ***
Library Selenium2Library
Library Selenium2Screenshots
Suite Teardown Close all browsers
*** Variables ***
${BROWSER} Firefox
*** Keywords ***
Highlight heading
[Arguments] ${locator}
Update element style ${locator} margin-top 0.75em
Highlight ${locator}
*** Test Cases ***
Take an annotated screenshot of RobotFramework.org
Open browser http://robotframework.org/ browser=${BROWSER}
Highlight heading css=#header h1
${note1} = Add pointy note
... css=#header
... This screenshot was generated using Robot Framework and Selenium.
... width=250 position=bottom
Capture and crop page screenshot robotframework.png
... css=#header ${note1}