Google increasingly uses various unauthorised third-party images in its horizontal Web Search and its specialised services like Google Images. It increasingly uses on-line images without the rightholders' consent, sometimes even against their explicit will. The search engines present images in full-size and high resolution on their sites and enable anybody to download them without ever having to click through to the original website hosting the image.
Although on many occasions, users might want their images to appear in search results, according to CEPIC (Center of the Picture Industry), 85% of pictures found online by visual search systems are unlawful copies and 80% of those images have been spread through search engines.
Although photographers and website owners have full control over their images, through various plugins and using a robots.txt file, there is often a lack of awereness about it.
So within the Media Library, it might be a nice idea to have an additional option to "Discourage search engines from indexing this image", and then users can be aware of this straight away and decide whether or not they want any of their images included in image searches or web searches.