How to serialize an object that includes BufferedImages

make your ArrayList<BufferedImage> transient, and implement a custom writeObject() method. In this, write the regular data for your ImageCanvas, then manually write out the byte data for the images, using PNG format.

class ImageCanvas implements Serializable {
    transient List<BufferedImage> images;

    private void writeObject(ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        out.writeInt(images.size()); // how many images are serialized?
        for (BufferedImage eachImage : images) {
            ImageIO.write(eachImage, "png", out); // png is lossless
        }
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        final int imageCount = in.readInt();
        images = new ArrayList<BufferedImage>(imageCount);
        for (int i=0; i<imageCount; i++) {
            images.add(ImageIO.read(in));
        }
    }
}