I have had a loss of between 50 and 75% on my two blogs, and I am almost sure it is due to the new Google image search. In the past, if somebody clicked on a picture, he came to your blog to see its enlarged version or its context. Now he sees the enlarged version there, on Google.
To give you an example, on my blog I had various models of job search papers. These got up to 2000 hits a day which allowed me to publish poetry and even religious things.
Now Google publishes 1 of my models at the top of the page. It is not the best, and it is not representative, but people see it full size and there is nothing to tell them that on my site there are more.