Notes from the Google Webmaster Hangouts on the 23rd and 26th of August, 2016.
Canonicalise PDFs to Web Pages
If you want to Canonicalise PDF pages to their desktop equivalent, you can include the canonical link in response headers.
Image Search Uses Page Content
Image search uses the content of the page hosting the image, along with the image, which is combined for the image search results.
Google Only Uses Click Behaviour to Assess Algorithms
Google aggregates user data to broadly assess algorithms, but John says they don’t affect individual page’s rankings.
Google Cache Doesn't Represent Indexed Content
You should do a site search query with a related keyword to check if content has been correctly indexed.
Any Type of HTTPS Certificate is OK
Any type of HTTPS certificate is valid including free ones.
Mobile URLs Should Not Appear in Desktop Search
If you are seeing mobile specific pages in desktop search, then it means the configuration is not right. They should be canonicalised to the desktop page, and therefore are technically not indexable.
Google Recommend Responsive or Dynamic over Dedicated Mobile URLs
Google supports all 3 variations, but recommends responsive design as it is easier to get the configuration right.