Wraith uses either PhantomJS, CasperJS and SlimerJS to create screen-shots of webpages on different environments and then creates a diff of the two images, the affected areas are highlighted in blue.
Wraith is a Ruby gem with a simple command line interface for developers, testers or anyone interested in visual regression testing. Wraith can select entire pages, or a specific CSS selector on a page for targeted testing of components across multiple pages and environments.
Wraith has several modes of operation, direct comparison of 2 websites, a history mode for rapid developer feedback or a spider mode for crawling a website.