As an example, let's take the above PowerPoint presentation that contains unseen aerial photographs of the World Trade Center captured by a military chopper on 9-11.
To extract pictures from the PPT slideshow, all you have to do is export the Powerpoint Presentation as an HTML web page. Choose File -> Save As and select .html from the File Format drop down.
PowerPoint will automatically extract every picture embedded in the PPT file and save it to the local folder. The same technique is also used to extract sound from presentations.
Alternatively, you may choose File -> Save As and choose an image format like JPG or PNG - this will save the entire presentation slides as numbered images.
Related: How to Compress PowerPoint Files