In recent years, a number of image encryption schemes based on DNA coding and nonlinear dynamics have been proposed. Generally, these DNA-based schemes first encode plaintext images into DNA sequences and then encrypt them with pseudorandom elements produced by chaotic systems or other nonlinear dynamics. Although ciphertexts can pass some security tests, many image encryption schemes are being shown to have intrinsic flaws and that they cannot guarantee a high level of security. In this paper, we cryptanalyze a family of image encryption schemes for which the encryption kernel is DNA coding or its variant. The complex DNA operation can be simplified as a substitution box (S-box). The whole cryptosystem's security level is thus significantly decreased and is vulnerable to the chosen-plaintext attack. Applications of this concept to break five ciphers are theoretically presented and experimentally verified. In addition, some suggestions for resisting similar attacks are also given in this paper.