The researcher has adopted a digital watermarking technique which operates in the frequency domain: a hybrid watermarking scheme based joint discrete wavelet transform -discrete cosine transform -(DWT-DCT). Its main objective is to test whether this technique can withstand attacks (its robustness) and invisibility (its imperceptibility), achieved by taking DCT of the DWT coefficients of the LL mid-frequency sub-bands from its band. To ensure security, the secret code (watermark) is scrambled using the Arnold transformation which is embedded in the original host image; only gray-scale digital images are used. The results of this research reveal that the secret code (watermark) is strong enough against threats (noise). Comparative results are measured using signal-tonoise ratio criterions, mean square error and normalized cross correlation. Simulated experimentation is done in Matlab.