Updating the referral source
For webmasters, it hasn’t always been easy to understand the role Google Images plays in driving site traffic. To address this, we will roll out a new referrer URL specific to Google Images over the next few months. The referrer URL is part of the HTTP header, and indicates the last page the user was on and clicked to visit the destination webpage.
If you create software to track or analyze website traffic, we want you to be prepared for this change. Make sure that you are ingesting the new referer URL, and attribute the traffic to Google Images. The new referer URL is: https://images.google.com.
If you use Google Analytics to track site data, the new referral URL will be automatically ingested and traffic will be attributed to Google Images appropriately. Just to be clear, this change will not affect Search Console. Webmasters will continue to receive an aggregate list of top search queries that drive traffic to their site.
— Read on webmasters.googleblog.com/2018/07/an-update-to-referral-source-urls-for.html