Digital Watermarking of Medical Images - Proceedings of All India Seminar on Biomedical Engineering 2012 (AISOBE-2012) - page 106

in computers, but also transferred across networks and with advent of cloud
computing sometimes stored on network clouds. In such a scenario, there is a
chance of images getting distorted on the way. Even stored images can be distorted
due to activities of hackers and malicious software like malwares and viruses. The
distortion may not severely affect the image, but will make its user skeptic toward
originality of image. Therefore, the distorted images are of no use to medical
professionals and also cannot be used as a proof in legal matters before the law.
The digital watermarking techniques discussed here would reinstantiate the orig-
inality of images after transmission over a network or if the images are stored for
very long. Reference [ 1 ] provides a detailed description of medical security.
Classification of different watermarking techniques is provided first and then we
cover the details of the watermarking method that we have used.
Classification
Digitally watermarked images can be classified on various grounds depending on
the different aspects of watermarking. One classification is made on the robustness
of watermarking; a watermark is said to be fragile if it gets changed, if any change
is made to image. On the other hand, a watermark is said to be robust if it can
survive attacks like compression, cropping, etc.
Another classification can be made on the basis of the technique used in
watermarking. If image pixel information is changed to create a watermark, it is
known as the spatial domain technique. Sometimes, image is transformed into
frequency domain using transforms, of which are the well-known Fast Fourier
Transform (FFT), Discrete Cosine Transform (DCT) and Discrete Wavelet
Transform (DWT). Such techniques are called frequency domain techniques.
Watermarking techniques can also be classified as reversible and non-reversible.
When it is possible to get the original image from the watermarked one, the
method is said to be reversible or else it is non-reversible watermarking. Other
classifications can be made on the basis of whether watermark is included in the
region of interest (ROI). If watermark is embedded in ROI it should not affect the
medical detection, hence some of the techniques decide an ROI and embed
watermarking in the non-ROI region.
Spatial Domain Techniques
Spatial domain techniques of watermark embedding which modify the pixel
information of image and thus provide watermarking are fragile techniques. The
watermark is sometimes embedded in LSB of every image pixel, thus creating
digital watermark but keeping the image usable. These techniques could be both
reversible as well as non-reversible.