To improve the encryption efficiency and security of images, this study proposes an optical double-image encryption method based on fingerprint keys. First, two grayscale images to be encrypted are modulated by two fingerprint-based random-phase masks, one placed at the input plane, the other at the Gyrator transform plane. The modulated results are then Gyrator transformed and combined into a complex-valued image. Subsequently, the encrypted image and two phase keys are obtained via phase-amplitude truncation on the complex-valued image. During the decryption process, the decryption key can be any of the following: the fingerprint, either phase key obtained by amplitude truncation, initial values and control parameters of the chaotic map, or parameters of the Gyrator transform. In the proposed encryption method, the secret key is associated with user identity, thereby enhancing system security. It also allows more convenient management of the secret keys because the phase-mask keys do not need to be transmitted over the network. Numerical simulations indicate the feasibility of the proposed encryption method and its high security and robustness against various attacks.