An image processing apparatus includes an image compression device which performs a discrete wavelet transform of pixel values for each rectangular portion to produce wavelet coefficients, and performs a hierarchical compression coding of the wavelet coefficients for each rectangular portion so that a codestream is produced. A codestream transform device is provided to reduce an amount of code data in the codestream. The codestream transform device comprises a syntax analysis unit which analyzes header information of each rectangular portion in the codestream. A comparison unit determines a similarity of pixel values between a current frame and a preceding frame in the codestream based on a result of the analysis. A codestream generating unit deletes code data of a corresponding rectangular portion of the current frame when the similarity is larger than a given threshold value.