if for example you where selling red shoes and your keyword was red shoes, you would have an image on your site. But you must have the alt tag set as follows: alt-"red shoes" following the url of the image, providing on the page you have the keyword "red shoes" in h1, h2 and h3 tags you should get the image indexed in google. Don't forget to have the kw in the last sentence
Just give the keyword in ALT image option, it will be definitely crawl by the Google bot. You can also share your website images on photo sharing site with the relevant keywords. Like picasa..