I frequently break my site in ways that aren't obvious. Right now, I use a combination of visualping and a homebrew tests.sh that hits various endpoints and runs checks, but I have been meaning to integrate screenshoting into my tests script (via selenium or cutycapt) rather than relying on a hosted service.

Have you found a good way of diffing the screenshots? DiffPDF works pretty well, but I haven't found a good solution for checking whether there are relevant changes automatically, rather than just has-changed, in a way that could be integrated into a script.