A digital watermarking method for medical images resistant to print-scan based on QR code

Medical images are important records to improve people's health care, and their security has become an important issue when they are transmitted through various media especially print and scan equipments. This paper proposes a digital watermarking method for medical images based on live QR code, DWT-SVD, Hough transform and bilinear interpolation. A live QR code including private information was embedded into the SVD blocks of LL3sub-band wavelet of medical image. Adjusting the embedding strength, a trade-off between invisibility and robustness was achieved. We printed and scanned the watermarked medical image with common printers and scanners and get the watermarked images after print-scanning. In extraction method, the Hough transform was used to detect the edge of the watermarked medical image and calculate the rotation angle and scaling ratio, and bilinear interpolation was used to correct geometric distortion of watermarked image. Then we extracted live QR code from corrected image successfully. Experimental results indicated that the proposed method provides sufficient security for medical images against print and scan attacks.