you don't have to include direct patch of you image for sitemap.. SEs still going to crawl to indexed it..
Why not just create an image xml sitemap? (e.g. using A1 Sitemap Generator or similar tools can create image sitemaps for Google search engine)
Sitemap is meant only for links.. not for images... images are not going to lead anyone thru yur site..
And including images in sitemap is not necessarily needed to index them, Google has it's own kind of crawlers to index them.
If your aim is to get images indexed on search engines, make effective use of ALT tags.Dont worry about the rest.Your images will automatically crawled.Compressing your images to reduce their size will greatly help you to be on first few SERPs though there are images existing already with the same keyword in alt tag.
It's simple to check Google http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=178636 Years ago Google added their XML sitemaps extension, "image sitemaps"
you can also add images on site maps like this: <image:image> <image:loc>http:// example.com/image.jpg</image:loc> </image:image>
There was a site that was providing a script i think it is called xml sitemaps and you can add and videos and more, they released it few days ago, the latest version.
I have tried to do this but is not effective, so I recommend you skip this idea to avoid losing time!