I would be guessing but I would say an EPS often renders badly since the screen shows a low-res bitmap and the format behind it prints in high resolution.

However, the file format of pptx is actually a zip file and you can open it with a zip tool and look inside and see all the graphics sitting in a folder. I don't know how you do this on a Mac but it is pretty simple on a PC. If the graphic came from a PC originally, you might be able to figure out the graphic format by its file extension.

__________________
Andrew Lockton
Chrysalis Design, Melbourne Australia