Resolved Digital Photo Format Changes

PPS is n ot an image format, it's PowerPoint Presentation format.
Presentation may contain various images of different image formats.

If you have Microsoft Powerpoint go to the File Menu and do SaveAs and save as HTML and the individual images will get exported.

If don't have Powerpoint you'll need a 3rd party software that extracts images from Powerpoint files.

You could also install the free OpenOffice.org suite. It has a presentation program called Impress which can open the Powerpoint files and dump the images in them.