Selenium WebDriver’s screenshot implementation varies depending on the browser’s WebDriver and browser version. This is not to be confused with the automated screenshots Sauce Labs takes of tests as they are run. Check out the information on our implementation of the Selenium screenshot testing option in the Test Configuration Options topic in our wiki.
Browser/WebDriver Combinations that Take Full Page Screenshots
Full Page means that the entire HTML page is captured, regardless of what is rendered as visible on the browser itself. Firefox version 47 and below (which all use FirefoxDriver) and all versions of Internet Explorer take full page screenshots. However, with IEDriver version 2.41.0, screenshots will sometimes have black bars on the image. If you have to use this older version of the IE Driver, you can work around the problem by specifying a 64 bit version of the IE driver in the capabilities, like this:
This workaround is not necessary for IE 9 on Windows 7, as the screenshots work as expected on 2.41.0.
Browser/WebDriver Combinations that Take Partial Page Screenshots
Partial Page means that the screenshot captures only the currently visible portion of the viewport. This will vary with the resolution of the VM and how the browser renders the page. It's more likely the screenshots will be partial for these browser/webdriver combinations:
Firefox 48 and above (which all use Geckodriver).
Known issues with screenshots: https://github.com/mozilla/geckodriver/issues/265
Chrome (all versions)
Known issues with screenshots: https://code.google.com/p/chromedriver/issues/detail?id=294
Safari (all versions)
Known issues with screenshots: https://code.google.com/p/selenium/issues/detail?id=3752