Multimedia security is ever demanding area of research covering different aspects of electrical engineering and computer science. In this chapter, our main focus is encryption of JPEG2000 compatible images. Though both stream and block cipher have been investigated in the literature, but this chapter provides a detailed study of block cipher as applied to images, since JPEG2000 generates various subband sizes as blocks. In the first section, we briefly define various encryption components like wavelet transform, bit plane decomposition, XOR operation, artificial neural network, seed key generator and chaotic map functions, for interest of the reader. Later in Sect. 2, we present literature review of various encryption techniques from two perspectives: applications to highlight scope of research in this domain; and approaches to provide overall view of multimedia encryption. The section three provides a new two-layer encryption technique for JPEG2000 compatible images. The first step provides a single layer of encryption using a neural network to generate a pseudo-random sequence with a 128-bit key, which XORs with bit planes obtained from image subbands to generate encrypted sequences. The second step develops another layer of encryption using a cellular neural network with a different 128-bit key to develop sequences with hyper chaotic behavior. These sequences XOR with selected encrypted bit planes (obtained in step 1) to generate doubly-encrypted bit planes. Finally, these processed bit planes go through reverse process, followed by inverse wavelet transform to generate encrypted image. In order to test this approach, the section four presents commonly adopted testing criteria like 0/1 balancedness, NIST statistical test, correlation and histogram tests done on seed generator and encrypted images to demonstrate robustness of the proposed approach. It is also shown that the key size is above 256 bits.