Map<BufferedImage, Map<ImageTransform, Set<Point>>> map

ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file));
    for (BufferedImage image : map.keySet()) {
        ImageIO.write(image, "PNG", out);  // write the image to the stream
        out.writeObject(map.get(image));   // write the 'value' part of the map
    }

ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
    while(true) {
        try {
            BufferedImage image = ImageIO.read(in);
            Map<ImageTransform, Set<Point>> value =
                (Map<ImageTransform, Set<Point>>) in.readObject(); // marker
            map.put(image, value);
        } catch (IOException ioe) {
            break;
        }
    }

java.io.OptionalDataException
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1300)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:368)

public class ImageHolder implements Serializable {

    BufferedImage image;

    public ImageHolder(BufferedImage image) {
        this.image = image;
    }

    private void readObject(ObjectInputStream stream)
            throws IOException, ClassNotFoundException {
        image = ImageIO.read(stream);
    }

    private void writeObject(ObjectOutputStream stream)
            throws IOException {
        ImageIO.write(image, "PNG", stream);
    }

    private void readObjectNoData() throws ObjectStreamException {
        // leave image as null
    }