To enhance the security of a dot-matrix hologram (DMH), a method to hide an image inside the DMH is proposed. The hidden image, which does not depress the visibility and the dynamic-effect feature of the DMH, is invisible but can be reconstructed by illuminating the DMH with a specified laser beam. The reconstructed hidden image is invariable to the lateral shift between the laser beam and DMH. Two experiments are carried out to illustrate the applicability of the proposed method. © 2002 Society of Photo-Optical Instrumentation Engineers.