The following post is taken from the Google Press Office.
Every day, hundreds of millions of people use Google Images to visually discover and explore content on the web. Whether it be finding ideas for your next baking project, or visual instructions on how to fix a flat tire, exploring image results can sometimes be much more helpful than exploring text.
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 referer URL specific to Google Images over the next few months. The referer 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.
We hope this change will foster a healthy visual content ecosystem. If you’re interested in learning how to optimize your pages for Google Images, please refer to the Google Image Publishing Guidelines. If you have questions, feedback or suggestions, please let us know through the Webmaster Tools Help Forum.
The new referer URL has the same country code top level domain (ccTLD) as the URL used for searching on Google Images. In practice, this means that most visitors worldwide come from images.google.com. That’s because last year, we made a changeso that google.com became the default choice for searchers worldwide. However, some users may still choose to go directly to a country specific service, such as google.co.uk for the UK. For this use case, the referer uses that country TLD (for example, images.google.co.uk)