There is also Sikuli http://sikulix.com (Desktop-based) and Kantu https://kantu.io (Chromium-based) for visual regression testing. While these two are primarily for automation, one can use the FIND (image, similarity) commands to compare certain parts of the website with given templates.

Depending on the use case, checking just key parts of the website can even work better and create more stable test cases than whole website checks.