Think this will do what you want:
1) Save the pps file to disk.
2) Open Powerpoint programme and load presentation without running it.
3) Using the ‘view’ icons at bottom left go to ‘slide view’ (middle of the five icons)
4) Select and open the required slide, click on picture, right click and copy.
5) Open Paint program, Edit, Paste
6) File, Save As, choose destination, name and in ‘Save as type’ box change from bitmap to JPEG.
7) Click Save.
Hope this helps.