You can get complete idea from this source. create image sitemap http://www.microsystools.com/products/sitemap-generator/help/image-xml-sitemaps/
With image search, just as with web search, Google's goal is to provide the best and most relevant search results to our users. Following Google's Webmaster Guidelines and best practices for publishing images can increase the likelihood that your images will be returned in those search results. In addition, you can also use Google's image extensions for Sitemaps to give Google additional information about the images on your site's URLs. Doing this can help Google discover images we might not otherwise find (such as images that are reached via JavaScript forms), and also enables you to identify the most important images on a page. For example, if your site uses templates, every page might feature a boilerplate image. By not listing this image in your Sitemap, you're telling Google that it's less important than the images you have included. However, Google doesn't guarantee that we'll index all of your images or use all of the information in your Sitemap.
Is your website build on any CMS platform like Wordpress or Joomla? If yes then you can look on their extensions section and will find relative plugins to setup and generate the sitemap for your website