A Blind Watermarking Algorithm Based on DCT

The paper presents a blind digital image watermarking algorithm in the DCT domain, which use a average value of DCT coefficient as a threshold to realize the watermark embedding. In the process of embedding the watermark image is processed by Arnold transformation and the original image is divided into some blocks which are transformed into coefficients in the DCT domain. The average value of coefficients selected from the same location in DCT blocks is calculated and the selected coefficient in each DCT block is modified into a value which is not less than the negative threshold or not more than the positive threshold according to the Arnold transformed watermark value. The original carrier image is not needed in the process of watermark extraction. The experimental results show that the algorithm has good imperceptibility and is robust against the common image processing such as JPEG compression, filtering, noise contamination, cropping and scaling.