PowerPoint Image Copier is a nice free software to extract Images from PowerPoint presentations. It saves the extracted images as JPG files.
It is possible to extract images directly using PowerPoint as well, but the quality of extracted images is not very good. PowerPoint to Image copier extracts image of much better quality. See sample below.
It is very easy to use, and you do not need to install anything. Just double-click on the icon, and the option window will come up. In that, specify the prefix for the extracted images, and then specify the path of your PowerPoint file. PowerPoint Image copier will then extract all the images from PowerPoint file.
PowerPoint image copier works on both ppt as well as pps files. It does requires that PowerPoint should be installed on your computer.
Download using links at the end.