//Instantiate a Presentation class that represents the PPTX file
Presentation pres = new Presentation("data/presentation.pptx");

//Access the first slide
ISlide sld = pres.getSlides().get_Item(0);

//Create a full scale image
BufferedImage image = sld.getThumbnail(1f, 1f);

//Save the image to disk in JPEG format
ImageIO.write(image,"jpeg",new File("data/AsposeThumbnail.jpg"));