Merge image in Java

Presentation pres = new Presentation();
try {
    pres.getSlides().removeAt(0);
    pres.getSlides().addFromHtml(new FileInputStream("file1.html"));
    pres.getSlides().addFromHtml(new FileInputStream("file2.html"));

    for (int index = 0; index < pres.getSlides().size(); index++)
    {
        ISlide slide = pres.getSlides().get_Item(index);
        IImage image = slide.getImage();
        image.save("image_java_" + index + ".png", ImageFormat.Png);
    }
} finally {
    if (pres != null) pres.dispose();
}