Google is updating the referrer URL from Google Image search in the upcoming months. This is super important news for anyone who has any web site that uses any form of analytics to track their incoming traffic. Those who use Google Analytics and nothing else, do not need to worry about this. But others might need to, espesially those that built their own analytical tools.
The new referer URL is: https://images.google.com so when you get traffic from https://images.google.com you will clearly know it is coming from Google Image search.
Google did outright say that the current and old referrer made it super hard for one to know where their traffic was coming from - what is core web search or image search. This will help Google said:
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.
Of course, images found within web search will still be counted as from web search, as John Mueller from Google explained:
Correct -- when they're shown in the general web-search results, we count them as a part of web-search.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) July 18, 2018
Anyway, this is important to take note of. Google did not give us a specific cut over date, outside of saying in the next few months or so.
Forum discussion at Twitter.