To prevent images from your site appearing in 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
The next time Google crawls your site, we'll see this directive and drop your image from our search results.
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. It will also prevent cropping of the image for display within Mobile Image Search, as the image will be completely removed from Google's Image index. If you would like to exclude the images from all Google searches (including Google web search and Google Images), specify User-agent Googlebot.