WordPress.org offers interesting and not officially documented feature allowing you to get screenshots from any URL. There are not many options available, but for most things it will work just fine and save you a lot of time to make such sreenshots yourself. So, here is how to use it with xScape theme.
xScape allows you to upload images use WordPress Media Manager, use external images or download image from external URL. All images are resized and cached as needed by the framework. This tutorial has more info on what’s the best practice.
Installation of themes based on xScape theme framework is easy and not much different from regular themes. First activated, theme will try to set everything automatically, but that can fail, and than you will get the error report with the link to the solution.
xScape allows you to upload images, use external images or download image from external URL. Also, all images are resized as needed by the framework, and resized images are cached. This tutorial shows how you can do that on the example of the theme logo.