Actually Google has changed its format of Image Searching.....Now people won't have to visit the site to see the image....they can view it by staying at the Google page only.....Though Google is adding the link to the page from which the image is originated, but for users to visit the link to the page is quite unlikely....so the traffics, which u were getting from the image search on Google, are now gone.....that's y ur blog traffic has decreased dramatically. This new changes will mostly affect the photography related, blogs. Hope that helps