Online content delivery faces massive hurdles in the absence of a secure framework for protecting valuable data. Digital watermarking a technology that can be used for control, media identification, tracing and protecting content owner's rights provides the solution

This paper presents overview on digital watermarking and a new method that combines image encryption and watermarking technique for safe transmission purpose. This method is based on the combination of public private keys and secret key ciphering, and watermarking. The encryption algorithm with secret key is applied to the image. We encrypt the secret key with an encryption method based on public-private keys. Then, this secret key is embedded in the encrypted image. We apply and show the results of our method to medical images. 

The amount of digital medical images has increased rapidly in the Internet. The necessity of fast and secure diagnosis is vital in the medical world. Nowadays, the transmission of images became a daily routine and it is necessary to find an efficient form to transmit them over the net. In this paper we propose a new technique to encrypt an image for safe transmission. 

Our research deals with image encryption and watermarking. There are several methods to encrypt binary or grey level images. Watermarking can be an answer to make secure image transmission. For applications dealing with images, the watermarking objective is to embed invisibly message inside the image data. The length of the transmitted message can be relatively important, in fact, longer that just for identification. Insertion can be made in a different way according to the length of message or desired robustness. The combination in the spatial and frequency domains for the image watermarking is also possible.

An encryption method which depends on the secrecy of the encryption algorithm is not considered to be a true encryption method. In the same way, watermarking algorithms are well-known.

The encryption can be done by block or by stream. But the encryption block methods have presented two inconvenient applied to image. The first one was when you have homogeneous zones; all blocks of this kind are encrypted on the same manner. The second problem was that block encryption methods are not robust to noise. The stream cipher method is robust to moderate noise like JPEG compression with high quality factor. To embed the encrypted secret key in the image we have used a new DCT-based watermarking method. We have chosen to work in the frequency domain because of the robustness to JPEG compression of the stream cypher method. An important application is the secure transfer of medical image.

Firstly we present encryption algorithm per flux, then we explain how to apply to images this method, we describe the combination method. We apply the methods and the combination to medical images.