Yes, I know image file name is use as a keyword to get image rank but have you any other technique for image ranking.
well suppose you want to optimize a image as ranking or to get place on search engines....well put the image name with that keyword you want to optimize it...and while link building the anchor should have the particular keyword for hyperlink...in this way you will get the image ranking for the particular on image search listing. All the best
the image googlebot crawls even slower then the web googlebot so it takes a long time (maybe six months) for your site to get indexed. make sure you have alt tags for your images with your keywords. then all the other usual stuff applies: page title page file name the directory name the page is in bolded or header tags for keywords description for the page ect.