We propose a new image enhancement method for JPEG images on the Internet that a sender who has high resolution images embeds enhancement codes for representing high frequency DCT coefficients into low frequency DCT coefficients, and receivers recover either low resolution JPEG coded images by using conventional JPEG decoder or high resolution images by using code extraction from low frequency DCT coefficients. This image transmission method can be thought as so called steganographic communication in case that these enhancement codes are kept secret. In order to implement the steganographic image communication, after the DCT size is extended from 8×8 to 16 × 16, SNRs are measured for images not only with setting all high frequency coefficients greater than 8×8 size to zeros, then processing IDCT of 16×16 size, but also with processing IDCT of 8×8 size. A scanning method for high frequency DCT coefficients is also proposed. The simulation experiments show the amount of enhancement codes for recovering quantized high frequency DCT coefficients and SNRs without embedding enhancement codes into low frequency DCT coefficients.