Content Aware Retargeting of Stego Images

K. Thilagam, Ph. D. Research Scholar, Karpagam University, Coimbatore, India

Abstract

Images play a vital role in steganography, as cover media to hide secret messages. Retargeting becomes mandatory while transmitting  image  in  a  heterogeneous  network  because sender and recipient may not have display devices of same resolution. Resizing images by scaling or cropping also lead to  loss  of  visually  important  features.  In  steganography, resizing, compressing, and changing the color or format of stego images would result in loss of hidden information. In this paper we attempt to retarget stego images in a content preserving manner using a modified seam carving technique called  PSC.  Content  in  this  context  refers  to  the  visually salient  features  in  the  cover  image  as  well  as  the  secret message hidden within it. The cover image is first subjected to PSC  to  extract  as  many  seams  leaving  the  segments containing ROIs intact. Based on the size of secret message segment(s)  containing  the  ROIs  are  selected  to  encode  the secret message and is transmitted to the receiver. The seams are  also  encoded  separately  in  the  reverse  order  of  their extraction,  so  that  on  the  receiver  end  the  receiver  would download all the image segments containing the ROIs and as many seams as required to constitute an image that fits into the  target  device.  The  retargeted  image  contains  the  secret message intact which could be decoded by the receiver.