Visual cryptography aims to protect images against their possible illegitimate use. Thus, one can cipher, hash, or add watermarks for protecting copyright, among others. In this paper we provide a new solution to the problem of secret sharing for the case when the secret is an image. Our method combines the Shamir scheme for secret sharing using finite fields of characteristic 2 with the CBC mode of operation of a secure symmetric cryptographic scheme like AES, so that the security relies on that of the mentioned techniques. The resulting shares have the same resolution as that of the original image. The idea of the method could be generalized to other multimedia formats like audio or video, adapting the method to the corresponding encoded information.