You can view tutorial for image sitemaps if you follow my signature. But otherwise ask the developer of the sitemap builder tool you use
For one of my websites I had to create a php program to generate the sitemap. Here is why. I have about 31,000 shareware titles, each with its own page. So ... I had to iterate through the database and programmatically create a sitemap entry for each item.
There are various sitemap generators like A1 generator. Many more options are present. You can also create a PHP program to generate sitemap. You can try it.
As I said, I used to use A1 but it was trial and I am in no mood to buy a software for generating sitemaps of different kinds. What I asked is, is there anything similar open source?