As of May 8, Google has updated the Google Image Publishing Guidelines document, which adds some more details around structured data, page speed, title management and user experience details.
The newest iteration of the 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. Not only that, Google explained how the image titles work since the change.
Sections were added for adding structured data for product, video and recipe markup. There is even a section for speed, including information about their PageSpeeds Insights tool, AMP and responsive image techniques.