Notes from the Google Webmaster Hangout on the 21st of December 2018.
Image Sitemaps Help Google Understand Which Images You Want to Be Indexed
Google can find images to index in the source code, but Sitemaps can help them to confirm which images you want to be indexed.
Google Chooses a Higher Resolution Image Where Multiple Versions Exist
If you have both high and low resolution versions of images, Google will prefer the higher resolution version.
Google Re-Evaluates Pages if the URL Changes
If you move a page to a new URL, Google will re-evaluate it and the rankings may change temporarily.
Expect to See Rankings Drop When Sites Are Merged
If you merge websites, you should expect to see some rankings drop, as Google doesn’t just add up all the signals, and the pages need to be re-evaluated on the new site. Ensuring you have correctly redirected every page should help the signals be moved over.
Unlinked Brand Mentions Don't Pass Any Value
If a web page mentions your brand, but doesn’t link to your site, it won’t pass any value.
Block Staging Sites From Being Crawled by Google
You should block Google from indexing your staging site as it can cause problems. You can block access based on Googlebot’s user agent, or using robots.txt.
Unresolved Manual Action Penalties May Take Years to Expire
If you ignore a manual action penalty, it may take years to expire. You should try to fix the cause, and submit a reconsideration request.
Google Supports X-Robots Noindex to Block Images for Googlebot
Google respects x-robots noindex in image response headers.