Hiding message in JPG image

问题

I am trying to hide a in an image it's working fine with .bmp & .png but when I write image as JPG and try to retrieve the hidden message it is not working. My procedure, first read an image in format (bmp, gif, jpg,png) write message to hide and save it so that we can again read it and extract the message. When i save it with bmp or png it works fine but when saving with jpg and try to extract the message it doesn't work.

 ImageIO.write(bimg, "png", outputfile);//working
 ImageIO.write(bimg, "png", outputfile);//not working

What should I do to make it work for JPEG?

note: I am reading every pixel as 4 bit integer with ARGB value and changing LSB of R,G,B to hide message.

    public void stegnography(BufferedImage bimg,String msg,String filename)
    {

      int w=bimg.getWidth();
      int h=bimg.getHeight();
     //*************************************** 
     // String msg="Hide this message:)";
      System.out.println("message="+msg+" length="+msg.length());
    //*************************************** 

      if(msg.length()>255 )
      {
         jLabel3.setText("MESSAGE IS LARGE THAN 255 CHARACTERS");            
      }
      else if( msg.length()*11 >w*h)
      {
         jLabel3.setText("Image is too small");    
      }
      else{

  //-------------------------------------------
           byte[] msgbytes= msg.getBytes();

        int msglendecode= (bimg.getRGB(0,0)>>8)<<8;

         msglendecode |= msg.length();
        bimg.setRGB(0, 0,msglendecode );//hidig msg length at first position

         //System.out.println("\npixel at position (0,0) ");
         // bitpattern(bimg.getRGB(0,0) );

         for(int i=1,msgpos=0,row=0,j=0;   row<h   ;row++  )
      {
          for(int col=0;col<w && j<msgbytes.length ;col++,i++ )
          {      

               if (i%11==0) {

                    int rgb = bimg.getRGB(col,row);


                    int a=((rgb >> 24) & 0xff);

                    int r = (((rgb >> 16) & 0xff)>>3)<<3;
                    r=r|(msgbytes[msgpos]>>5);

                    int g = (((rgb >> 8) & 0xff)>>3)<<3;
                    g=g|((msgbytes[msgpos]>>2)& 7);

                     int b = ((rgb & 0xff)>>2)<<2;
                    b=b|(msgbytes[msgpos]&0x3);


                    rgb=0;
                    rgb=(rgb|(a<<24));
                    rgb=(rgb|(r<<16));
                    rgb=(rgb|(g<<8));

                    rgb=(rgb|b);

                    bimg.setRGB(col,row,rgb);

                    msgpos++;
                    j++;

                  //bitpattern(bimg.getRGB(col,row));

              }


          }//for 2
      }//for 1


      ImageIcon image = new ImageIcon(bimg);
           jLabel3.setIcon(image);  

     try {

  //  File outputfile = new File("c:/Users/yathestha/Documents/"+filename);
     File outputfile = new File("c:/Users/yathestha/Documents/outpng.png");
    ImageIO.write(bimg, "png", outputfile);
} catch (IOException e) {
         System.out.println("error in saving image ");
}

  //-------------------------------------------------
      }//else
 // decoding part----------------------------------------------------------------------   

    }
///////////////////////////////////////////////////////////////////////
private void decodestegnography(BufferedImage bimg) {

     System.out.println("in decode");

   int w=bimg.getWidth(),h=bimg.getHeight();
    bitpattern(bimg.getRGB(0, 0));
    int msglength=(bimg.getRGB(0, 0)&0xff);
    bitpattern(msglength);
    System.out.println("Message Length="+msglength);

    jTextField1.setText("");
      for(int row=0,j=0,i=1;   row<h   ;row++  )
  { 
      for(int col=0;col<w && j<msglength ;col++ ,i++)
      {

          if (i%11==0) {
             int result=bimg.getRGB(col,row);


              int charatpos = (((result >> 16) & 0x7) << 5);

              charatpos |=  (((result >> 8) & 0x7) << 2);

              charatpos |=  ((result & 0x3));

              jTextField1.setText(jTextField1.getText()+ (char)charatpos);

             j++;
          }
      }
  } 

     System.out.println("decoding done");
}//function

回答1:

For jpeg steganography either save your result as a lossless jpeg, or simply use a different stegographic method. The only one I know is fiddling with the Discrete Cosine Transform coefficients (DCT). However, you need to be aware of rounding errors and as such the retrieval of your secret will be lossy.

I don't favour DCT and I haven't looked into it a lot, but here is a paper from 2007 which claims jpeg lossless steganography. Be warned that the algorithm is much more complex than your casual LSB substitution in the spatial domain. Hiding data in the frequency domain also means lower hiding capacity and I don't know whether this will serve you. If you are interested and can't access the paper, we can sort this out privately.