Image steganography have been observed as one of the useful techniques to prevent unintended users to understand what information has been communicated over the network. Many crucial methods of image steganography include Discrete Cosine Transformation (DCT) based approaches. In this paper an efficient algorithm in image steganography is proposed extending DCT based approaches and incorporating number theory. The existing DCT algorithm is modified to increase randomness in the embedding technique with the help of Lucas sequence specifically. The effectiveness of the proposed method has been evaluated by computing Mean Square Error (MSE) and Peak Signal to Noise Ratio (PSNR). Results show that the proposed method has higher embedding capacity and increases a significant level of security by using Lucas sequence in addition to the advantages provided by existing DCT algorithm.