There are some early reports at WebmasterWorld of ranking changes and indexing changes within Google Image search.
The reports say that around November 15th and 16th some webmasters noticed a change in search traffic via Google Image search.
One webmaster said:
My image traffic has taken a bit of a dip since nov 16th(late 15th) and while trying to find a possible cause there doesn't seem to be one in my rankings/average positions of images etc.
This webmaster blames the new top navigation whereas another webmaster blames Google's indexing of images. He wrote:
One of my sites has had most of it's positions in google image traffic hijacked by different blogspots. My images are there, only credited to obscure blogs.
The last time we saw reports of a Google Image update was on October 1st.
Image updates are hard to spot since many webmaster do not track the results and traffic from image search.
Forum discussion at WebmasterWorld.