If the included code is run with the attached "thumb.jpg" image as its input, then a RuntimeException is thrown at line 18. This contravenes the specification as getRawImageType() is supposed to return the first element of the Iterator returned by getImageTypes() which is specified to include at least one element.

import java.io.File;
import javax.imageio.ImageIO;
import javax.imageio.ImageReader;
import javax.imageio.ImageTypeSpecifier;
import javax.imageio.stream.ImageInputStream;

public class ReadDimensions {
    public static void main(String[] args) throws Throwable {
        File file = new File(args[0]);
        ImageInputStream in = ImageIO.createImageInputStream(file);
        ImageReader r = ImageIO.getImageReaders(in).next();
        r.setInput(in);
        int w = r.getWidth(0);
        int h = r.getHeight(0);
        System.out.println(file + ": " + w + " x " + h);
        ImageTypeSpecifier its = r.getRawImageType(0);
        if (its == null) {
            throw new RuntimeException("ImageReader returns null raw image type"); // line 18
        }
    }
}