We already know that ALT tags should be used for relevant images (I say relevant because you can skip putting ALT tags for images placed in your page for purely aesthetic and/or organisational purposes such as borders). However, what many neglect to do is to take advantage of Google’s enhanced image search. The enhanced image search is actually very useful for helping the images in your pages rank better in Google images SERPs. Enhanced image search actually helps you rank better through the selection of labels that are more relevant to the images in your site. According to Google they are able to associate the image sin your site with relevant labels through the use of Google Image Labeler.
To opt-in to Google’s enhanced image search simply login to Google Webmaster Tools, choose the URL of the site you wish to have the enhanced image search enables, click Tools, and then click on Enable enhanced image search.
If you have a graphics intensive site you should really opt-in to this feature. If you worry that your images will rank better than your site and that users will end up simply ripping off your images (many actually do not visit the actual site but only go to the image URL) you can remedy this problem by redirecting users sent by Google. You can also disallow hotlinking of images.