## 2 Related Work
Medical images might include patient, disease, doctor or hospital information which is private information. In this work, wavelet and DCT frequency-based algorithms were used to hide this information in the region of interest to provide robust and secure hiding. The proposed watermarking algorithm was tested against Gaussian noise, salt and pepper noise, and median filter. The PSNR, mean secure error (MSE) and NC evaluation results were very promising. The medical data watermarking method enables the secure collection, storage and sharing of patient data. [PERSON] et al. [12] proposed a quantum D4 wavelet transform algorithm for images. Combining quantum wavelet transform and a controlled rotating gate produced promising results, especially for attacks. Lena, baboon, boat, man and sailboat images were tested with the proposed algorithm. The PSNR values were higher than 50 dB in all images, indicating greater efficiency than for other frequency and spatial domain algorithms. Simulation results showed that the proposed algorithm was feasible, effective and robust. [PERSON] et al. [13] worked on Canny-edge-detection-based watermarking, the edges being very critical pixels for hiding information. It is very difficult to identify, change and see the watermark, which is hidden in the edge of the image. The embedding process does not distort the image [14; 15]. DCT and SVD algorithms were used together in this work. The PSNR values were between 51 dB and 55 dB, which is very strong when compared with embedding with DCT or SVD. The binary image was embedded into the Lena, baboon,airplane, splash and girl images using the proposed algorithm. The proposed work was resistant against histogram equalization and JPEG compression attacks [16; 17; 18; 19]. There are also variations in authentication types of watermarking. Some fields, such as medicine or military, might require exact authentication. In exact authentication, even a bit change in the watermarked image causes the authentication to fail. Usually an image signature or a hash of the image is computed from some part of the image and stored in another part of the image. As is known, even a bit value change in the image will yield a completely different hash value to the embedded hash value. Exact authentication is also known as fragile authentication--there are many studies concerning fragile types of watermarking in the literature. One of the first studies of authentication-type image watermarking was carried out by [PERSON] et al. [20]. In this study, gray-level values [0...255] were mapped to binary values 0, 1 and this mapping was the key for watermark extraction. The binary watermark was inserted into the host image where the gray-level value was changed with the nearest value having the same mapping to the desired watermark bit value (0 or 1), or remained the same if the current gray-level value mapped to the desired watermark bit. [PERSON] et al. 's work [21] used a similar approach in which they mapped DCT domain values to binary values 0,1 instead of to pixel gray-level values. Subsequent to [PERSON] and [PERSON]'s work, several articles were published which showed that mapping of gray-level values can be attacked easily [22; 23]. [PERSON] and [PERSON]'s work [21] also has the same kind of weakness. [PERSON] and [PERSON] in [24] studied the uses of watermarking in authenticating medical images and ensuring their security. Generally, the least significant bits are used for authentication-type watermarking. [PERSON] et al. in [25] divided the image into non-overlapping 4 \(\times\) 4 blocks and further divided each 4 \(\times\) 4 block into 2 \(\times\) 2 sub-blocks, firstly setting the least significant two bits of pixels of the block to zero, calculating the parity and authentication bits using the difference between the mean intensity levels of the sub-blocks. Using a mapping algorithm, the authors made pairs of 4 \(\times\) 4 blocks, and a 6-bit length mean intensity value of one block was inserted into the least significant bits (LSBs) of the corresponding block.