A new optodigital multiple information hiding and real-time extraction system is suggested. In the proposed system, multiple information is hidden in a cover image by using stego keys, which are generated by combining use of a random sequence and Hadamard matrix. This hidden data is then extracted in real time by using an optical nonlinear joint transform correlator (NJTC)-based decoding system. In the experiment, 50, 30, and 20 combination sets of three letters selected from the English and Korean alphabets, and Arabic numerals are used as the multiple message data and they are formulated into 8×8 blocks, in which each block is composed of 64×64 pixels and multiplied with the corresponding stego keys of 64×64 pixels one by one. Then, by adding these modulated data to the cover image of Lena of 512×512 pixels, a stego image is generated. To extract the hidden data from this stego image in real time, an optical NJTC is employed, in which optical correlation between the stego image and each of the stego keys is performed, and from these correlation outputs the hidden data can be extracted. Computer simulations and optical experiments reveal that the proposed optical NJTC-based decoding system has a highly improved signal-to-noise ratio (SNR) performance of the correlation outputs under the condition of and these experimental results finally confirm the feasibility of the NJTC-based optical decoding system. © 2004 Society of Photo-Optical Instrumentation Engineers.