ImageReader reader = getImageReader(diskObject);
if (reader.readerSupportsThumbnails()) {
    if (reader.hasThumbnails(0)) {
        image = reader.readThumbnail(0, 0);
    } else {
        читаем картинку и делаем ей resize
    }

public class JPEGMetadata extends IIOMetadata implements Cloneable {
...  
    List markerSequence = new ArrayList();
...
    MarkerSegment findMarkerSegment(int tag) { ... }
...
}

class MarkerSegment implements Cloneable {
...
    byte [] data = null;  // Raw segment data, used for unrecognized segments
...
}

    private static byte[] findMarkerData(ImageReader reader, int tag) {
        try {
            IIOMetadata jpegMetadata = reader.getImageMetadata(0);
            if (jpegMetadata instanceof JPEGMetadata) {
                Class msClass = JIUtility.class.getClassLoader().loadClass("com.sun.imageio.plugins.jpeg.MarkerSegment");
                Method findMarkerSegment = jpegMetadata.getClass().getDeclaredMethod("findMarkerSegment", Integer.TYPE);
                findMarkerSegment.setAccessible(true);
                Object markerSegment = findMarkerSegment.invoke(jpegMetadata, tag);
                Field msData = msClass.getDeclaredField("data");
                msData.setAccessible(true);
                return (byte[]) msData.get(markerSegment);
            }
        } catch (Exception ex) {
            logger.log(Level.SEVERE, null, ex);
        }
        return null;
    }