Stephen Hay recommends rapid prototyping. In the workflow he'll use full screen webpage captures. As an alternative to the .js capture method you could install a web page capture app on your browser. "ExtensionFull Page Screen Capture" can do this. And here's a shot of a recent style tile:
If you use the Web Developer tools and watch the webpage in some mobile device the "ExtensionFull Page Screen Capture" is able to grab such a page too.
Hay propose to use such images in a pitch at an early stage of the web developent process. Here I have combined the idea with style tiles.