To remove an image from Google's image index, add a robots.txt file to the root of the server that blocks the image.
For example, if you want Google to exclude the dogs.jpg image that appears on your site at www.yoursite.com/images/dogs.jpg, add the following to your robots.txt file:
User-agent: Googlebot-Image Disallow: /images/dogs.jpg
To remove all the images on your site from our index, place the following robots.txt file in your server root:
User-agent: Googlebot-Image Disallow: /
Additionally, Google has introduced increased flexibility to the robots.txt file standard through the use asterisks. Disallow patterns may include "*" to match any sequence of characters, and patterns may end in "$" to indicate the end of a name. To remove all files of a specific file type (for example, to include .jpg but not .gif images), you'd use the following robots.txt entry:
User-agent: Googlebot-Image Disallow: /*.gif$
By specifying Googlebot-Image as the User-agent, the images will be excluded from Google Image Search. If you would like to exclude the images from all Google searches (including Google web search and Google Images), specify User-agent Googlebot.