There was a massive bug with Google Image search for the past four days that prevented searchers from clicking on an image to see the enlarged version.
The complaints started flowing in on Thursday, January 26th, via the Google Web Search Help forums an was only fixed several hours ago.
The issue was, if you clicked on an image in the list of images Google gives you for an image search results page - it would do nothing. It worked spontaneously some people said. It had issues in Chrome as well as other non-Google browsers.
Here is a screen shot from one of the users with the issue:
I wonder how much of an impact this had on webmasters who receive a lot of image traffic to their web sites?
The issue is supposedly fixed according to top contributor bluequoll who said "I've been advised that this issue should now be resolved."
Forum discussion at Google Web Search Help.