Google updated the Google Image Publishing Guidelines document today, adding more details around structured data, page speed, title management and user experience details. The old documentation can be viewed in this screen shot I captured previously.
The new guidelines have updated content around creating a better user experience with your images, including adding good context, optimizing placement, embedding tips, device-friendly sites and good URL structure for your images. In addition, Google has explained how the image titles work since the change.
Google also added sections for adding structured data for product, video and recipe markup. There is a new section for speed, including information about their PageSpeeds Insights tool, AMP and responsive image techniques.