Opto-electronic hybrid joint transform correlator is developed successfully utilizing the Fourier transform feature of lens and adopting key devices such as electrical addressed liquid crystal device (EALCD), which can realize quasi-real-time detection and precise location of targets with cluttered background. Compared to 4f system, it has the advantages of high identification accuracy, fast recognition speed and so on. However, the image information of moving targets collected form image sensor contains various forms of distortion (such as displacement, rotation and scale, etc.), which makes it difficult to realize automatic real-time recognition and tracking of moving targets. In this paper, the method of Mellin transform is proposed. The theory and algorithm of Mellin transform are studied deeply and computer simulation experiments and optical experiments are also conducted with good results. This solved the problem of scale invariable. As an example, the experiment results of aerial images taken at high altitudet are given. The size of target is 150% of the template. Brighter correlation peaks are obtained after Mellin transform. The algorithm has strong pratical application significance in the field of opto-electronic hybrid target detection.