  This paper introduces current watermarking techniques available from the
literatures. Requirements for medical watermarking will be discussed. We then
propose a watermarking scheme that can recover the original image from the
watermarked one. The purpose is to verify the integrity and authenticity of
DICOM images. We used ultrasound (US) images in our experiment. SHA-256 of the
whole image is embedded in the least significant bits of the RONI (Region of
Non-Interest). If the image has not been altered, the watermark will be
extracted and the original image will be recovered. SHA-256 of the recovered
image will be compared with the extracted watermark for authentication.
