1. A method of encrypting/embedding and decrypting/extracting a secret image, comprising the steps of: a) encrypting a secret image of N.times.M pixels with g.sub.ij gray levels using a chaotic map; b) choosing some carrier image of 2N.times.2M pixels with g.sub.ij gray levels; c) modifying said carrier image according to a pseudocode, including the further steps of: i) for each pixel P=(i, j) of the secret image, converting the gray level g.sub.ij to a base 4 representation, t1, t2, t3, t4, where t1+t2*4+t3*16+t4*64=g.sub.ij ; and ii) modifying the gray levels of pixels (2i, 2j), (2i+1, 2j), (2i, 2j+1), (2i+1, 2j+1) of the carrier image by 2-t1, 2-t2, 2-t3, and 2-t4, respectively; and d) sending said modified carrier image to a recipient.