Java URL: Unknown Protocol "C"

Try with

String imageUrl = "file:///C:/Users/MyUser/image.jpg";

Try this

try {
    String imageUrl = "file:///C:/Users/MyUser/image.jpg";
    Jpeg image = new Jpeg(new URL(imageUrl));
} catch(Exception exc) {
    System.out.println(exc.getMessage());
}

You need to turn the path to the image.jpg file into a file:// URL, like this:

String imageUrl = "file:///C:/Users/MyUser/image.jpg";

Otherwise it interprets the C as the URL protocol.