Search on images are very less and limited to few people especially designers & professionals on internet.
Considering the fact Google(images.google.com) places a tab on its search box is a big enough reason that image search has significant traffic, hence must be given importance by webmasters.
Depending on the keywords, Google even throws up image results in the beginning before first organic result on web search as well.
If your website contains images then you should optimize them for high results on search engines.
Use the same Google operators site:www.domain.com on images, images.google.com to check the list of images crawled & indexed across your site.