In this paper a novel "Discrete Cosine Transformation based Image Authentication"Secret Message Transmission Scheme" (DCTIASMTT) has been proposed to authenticate a multimedia image and at the same time some ubiquitous secret message or image can be transmitted over the mobile network. Instead of direct embedding a message or image within the source image, choose a window of size 2×2 of the source image and then convert it from spatial domain to frequency domain using Discrete Cosine Transformation (DCT). The bits of the authenticating message or image are then embedded at LSB of the transformed image (excluding first pixel). Inverse DCT has been performed for the transformation from frequency domain to spatial domain as final step of encoding. Decoding is done through reverse procedure. The experimental results have been discussed and compared with the existing steganographic algorithm S-Tools. Histogram analysis and Chi-Square test of source image with embedded image shows the better results in comparison with S-Tools. © 2009 IEEE.