A key element of the optical image processing system is an image memory to temporarily store a huge amount of information between processing. Attempts have been made to use a silver halide photographic plate, a non-linear photorefractive crystal, a liquid crystal display and other elements as the image memory. However, none of these elements has proved satisfactory with respect to the following criteria: write and erase by an electrical method, signal-to-noise ratio of stored images, size of memory area and optical resolution. A thermoplastic photographic plate (TPP), in view ofits advantages oflarge memory capacity and ability to write and erase electrically, has been used for real time holography. However, the TPP is subject to the drawback of a high signal-to-noise ratio and has not been suitable for the image memory of the optical image processing. Recently, the authors conceived three methods to eliminate the drawback, and applied the TPP to holographic defect detection in periodic patterns. The TPP was used as the image memory and defect images were separated by spatial filtering and holographic optical image processing. Our results showed that 0.09 pm defects can be detected with signal-to-noise ratio 3.