ESNEK RESİM DAMGALAMA: BLOK TABANLI DAMGALAMA ANALİZİ, VEKTÖR DAMGASI KULLANIMI VE DOĞRULAMA DAMGALAMASININ GELİŞTİRİLMESİ
Özet
As we live in a digital World, protecting our digital property and to be sure that the data we receive is the same as original has become more important. Digital watermarking emerged as a discipline to ensure copyright ownership and authenticating digital data.
The image is transformed into another domain, watermarked in this new domain and restransformed into pixel domain by applying inverse transform in most of the copyright protection and authentication type of watermarking algorithms. In the scope of this thesis, it is searched if it makes a difference between transforming an image to the new domain as a whole or dividing the image into blocks and transforming each block to new domain separately. It is examined if using block-based approach affects watermarking performance for different block sizes for DWT-based watermarking. It is revealed by this study that dividing the image into blocks beforehand, transforming each block to new domain separately, and then watermarking the blocks improves robustness drastically. It is also revealed by this study that as block size decreased, robustness increased with the cost of extra cpu time needed.
In most of the previous image watermarking studies, an image digest, a pseudo random number sequence, a binary image logo etc is inserted as a watermark. To the best of our knowledge a vector image is not used as a watermark before. A vector image is different from a binary image in that it does not consist of pixels but consists of points, circles, polygons, lines, beziers etc. All those items have their own attributes. For example, a circle has center point coordinates (x,y), diameter, line color, line width etc. Vector images’ quality does not suffer from scaling operations. In this thesis a vector image is embedded as a watermark in a robust way in DWT domain that survived jpeg compression, histogram equilization, 3x3 low-pass filter except cropping and rotation attacks.
The type of watermarking that pursues proving the image’s geunineness is image authentication type of watermarking. Fragile type of authentication purpose image watermarking is sensitive to every type and amount of change and does not discriminate the changes as ill purposed or innocent. In the scope of this thesis, a new fragile DWT-based authentication type of image watermarking algorithm is introduced. The method detects the changed region of the image successfully and it is easy to implement.
The ideal authentication type of watermarking is expected to be robust against innocent type of changes applied to the image and to be fragile against ill-purpose changes performed on the image. Lossy image compression applied to the image, scaling, sharpening, blurring, histogram equilization that affect all of the image can be given as examples of innocent type of operations to be performed on an image. Removing an existing person from an image, changing one’s face, changing a car’s licence plate, perform “man in the middle attack” can be given examples for the ill-purpose operations that can be performed on an image. The semi-fragile authentication watermarking method will approach the ideal form as the type of ill-purpose attacks it detects increases and authenticates the images that are subjected to innocent operations. In the scope of this thesis, a new semi-fragile authentication image watermarking method is built up that uses DCT and DWT domains, that embeds two watermarks to the image for copyright protection and authentication purposes. The built-up method authenticates %75 quality jpeg compressed images and in addition to the existing methods, authenticates images that are subjected to histogram equilization, intensity adjustment and gamma correction. The new method is also immune to collage attacks.
