Has Google Changed their Image Search Algorithm?

One of my site, which basically belongs to entertainment niche, with full of images was receiving more than 60% of its traffic from Image search engine. I was getting close to 800 referrals from google's different image seasrch engine (located in different places). Day before yesterday when I checked the analytics stats I was in for a surprise, the huge number of 700+ was reduced to a mere 90+. That was a shock as against usual trends people who visit via image search engine also spends good amount of time in my site. I checked the stats today also and was dissappointed by the falling image search numbers.


My traffic from google search engine still remain the same. This led me to the question whether Google has indeed change their image search algorithm. As a usual SEO technique I used to use alt tag along with all images. Since I group images as a set I use the same alt tag for one set. Google might be now penalizing guys who are using the same alt tags for more than one image. Another could be , google may have discarded the alt tag completely as there are widespread abuse of the same. This also could have occured because I used the PageName tag for title recently; this may result in search engine taking more time for re-analysing the pages. These are my assumptions, this may be wrong. But if anyone of you have experienced the same please comment. Anyway I am going to wait for some more days to see what happens. Would report the same in a couple of days.