SpeedCurve now provides a visual diff of every deploy. A full resolution PNG is captured for each URL and each pixel is diffed with the previous deploy allowing you to easily spot any visual changes you may or may not have expected.
The key to practising safe continuous deployment is to have a robust set of tools that give you immediate feedback on how your code has changed between deploys and its effect on the user experience. It's often very hard to spot all the visual changes in each deploy, especially in fast moving teams where a lot of the focus is on unit tests and other automated pass/fail systems. Visual diffs bring an increased level of tracking and confidence when you're able to compare any two deploys and see exactly what has visually changed.
We do a visual diff every time you click "Test Now" on the Deploy dashboard or you use the SpeedCurve API to trigger a round of deploy testing. Integrating with the Deploy API is super easy and provides a robust set of metrics and before/after screenshots, visual diffs, waterfall charts, filmstrips and videos for each deploy. You can then compare any two deploys to see exactly what's changed over time.