  The need of exchanging messages and images secretly over unsecure networks
promoted the creation of cryptosystems to enable receivers to interpret the
exchanged information. In this paper, a particular public key cryptosystem
called the ElGamal Cryptosystem is presented considered with the help MATLAB
Program to be used over Images. Since the ElGamal cryptosystem over a primitive
root of a large prime is used in messages encryption in the free GNU Privacy
Guard software, recent versions of PGP, and other cryptosystems. This paper
shows a modification of the this cryptosystem by applying it over gray and
color images. That would be by transforming an image into its corresponding
matrix using MATLAB Program, then applying the encryption and decryption
algorithms over it. Actually, this modification gives one of the best image
encryptions that have been used since the encryption procedure over any image
goes smoothly and transfers the original image to completely undefined image
which makes this cryptosystem is really secure and successful over image
encryption. As well as, the decryption procedure of the encrypted image works
very well since it transfers undefined image to its original. Therefore, this
new modification can make the cryptosystem of images more immune against some
future attacks since breaking this cryptosystem depends on solving the discrete
logarithm problem which is really impossible with large prime numbers .
