If you split the task "create thumbnail" into three steps, "load image", "scale image" and "save image", you can do it with the standard Java API. You can use the static utility methods in javax.imageio.ImageIO to load and save images and use Image#getScaledInstance(...) to resize the original image. Since the Image you get from getScaledInstance is not a BufferedImage, you have to create a new BufferedImage with the correct size and paint the scaled image into the new BufferedImage before you can use ImageIO to save it.
