In this paper a Z-transform based image authentication technique termed as IAZT has been proposed to authenticate gray scale images. The technique uses energy efficient and low bandwidth based invisible data embedding with a minimal computational complexity. Near about half of the bandwidth is required compared to the traditional Z–transform while transmitting the multimedia contents such as images with authenticating message through network. This authenticating technique may be used for copyright protection or ownership verification. Experimental results are computed and compared with the existing authentication techniques like Li’s method [11], SCDFT [13], Region-Based method [14] and many more based on Mean Square Error (MSE), Peak Signal to Noise Ratio (PSNR), Image Fidelity (IF), Universal Quality Image (UQI) and Structural Similarity Index Measurement (SSIM) which shows better performance in IAZT.