Attached Link: http://www.hdri.at/en/hdri_en.htm

Poser 6 doesn't use HDR images. The images it uses are low dynamic range (LDR), such as .jpg, .bmp, etc. Here's a good explaination of what HDRI is, and there's a link to some comparison images of LDR vs. HDR at the bottom of the page. Basically, HDR is a type of image-based lighting (IBL), which contains more brightness information than regular image formats, allowing for brighter brights and darker darks to be used as a lightsource.