I've been seeing posts and forum complaints that Google Analytics has shown tremendous drops in search referrals from Google Image Search. To make a long story short, Google Analytics seemed to have switched how they report Google Image search traffic, moving it from the referrals report and into the organic search report.
There are reports at WebmasterWorld (see July 26th) and Google Analytics Help forums about this.
As reported by Gabs and AJ Kohn, it is simply a matter of Google moving the traffic under the search engine report.
Here is a graph from Gabs:
I was able to verify this in several of my sites that I track.
Google, I do not believe, has any word about this change, so I can see why people freaked out when they saw this.
Forum discussion at WebmasterWorld and Google Analytics Help.
