I block the Google image spider on all of my sites. I have never believed that it delivers legitimate traffic. It only delivers image thieves.
You have a couple of choices using the robots.txt file
1. Block your images directories. If you use the image uploader with WordPress, add the following to your wildcard User-agent record and, if you use one, the User-agent: Googlebot record:
Some people use:
2. For other sites add this to the robots.txt file. It needs to be separate from your other User-agent records.
It may take a month or so, but Google will stop indexing your images.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin