As our own Jeff told you before, Awesome Screenshot, a desktop web app for Google Chrome, Firefox and Safari, is arguably the best way to capture an entire web page as an image on OS X.
Thanks to the various extensibility features introduced in iOS 8, this nifty little utility is now available as a screenshot extension for Safari on the iPhone, iPod touch and iPad devices running iOS 8.
Upon downloading the free app from the App Store, Awesome Screenshot will allow you to capture a screenshot of any webpage simply by choosing it in Safari's Share menu.
Not only can you capture images of web pages on mobile devices with ease, but also annotate and share them with others using Apple's stock sharing choices or a number of third-party Share extensions available in the App Store.