  Digital Retinal Fundus Images helps to detect various ophthalmic diseases by
detecting morphological changes in optical cup, optical disc and macula.
Present work proposes a method for the authentication of medical images based
on Discrete Wavelet Transformation (DWT) and Spread Spectrum. Proper selection
of the Non Region of Interest (NROI) for watermarking is crucial, as the area
under concern has to be the least required portion conveying any medical
information. Proposed method discusses both the selection of least impact area
and the blind watermarking technique. Watermark is embedded within the
High-High (HH) sub band. During embedding, watermarked image is dispersed
within the band using a pseudo random sequence and a Session key. Watermarked
image is extracted using the session key and the size of the image. In this
approach the generated watermarked image having an acceptable level of
imperceptibility and distortion is compared to the Original retinal image based
on Peak Signal to Noise Ratio (PSNR) and correlation value.
