In this paper a technique for the coding of digital images is developed using Fractional Wavelet Trans form (FWT) and random phase masks. The digital image to encrypt is transformed with the FWT, after the coefficients r esulting from the FWT (Approximation, Details: Horizontal, vertical a nd diagonal) are multiplied each one by different r andom phase masks (statistically independent) and these latest results is applied an Inverse Wavelet Transform (IW T), obtaining the encrypted digital image. The decryption technique i s the same encryption technique in reverse sense. T his technique provides immediate security advantages compared to conventional techniques: in this technique the moth er wavelet family and fractional orders associated with the FWT are a dditional keys that make access to information diff icult for an unauthorized person (besides the random phase masks used), thereby the level of encryption security is extraordinarily increased. In this work the mathematical support fo r the use of the FWT in the computacional algorithm for the coding is also developed.