BufferedImage myBI = //das BufferedImage
ByteArrayOutputStream myBAOS = new ByteArrayOutputStream();
JPEGImageEncoder myEncoder = JPEGCodec.createJPEGEncoder(myBAOS);
myEncoder.encode(myBI);
byte[] myByteArray = myBAOS.toByteArray();
InputStream myIS = new ByteArrayInputStream(myByteArray);
Öhm wüsste nicht warum man das wollte...
BufferedImage myBI = //das BufferedImage
ByteArrayOutputStream myBAOS = new ByteArrayOutputStream();
ImageIO.write(myBI, "jpg", myBAOS);
byte[] myByteArray = myBAOS.toByteArray();
InputStream myIS = new ByteArrayInputStream(myByteArray);