Recently, a variety of chaos-based cryptosystems have been proposed. Some of these novel chaotic encryption schemes are not very suitable for image encryption due to their density function which is not uniformly distributed or due to their small key space. In this paper, we propose a new scheme for image encryption based on the use of a chaotic map with large key space and Engle Continued Fractions (ECF) map. The ECF-map is employed to generate a pseudo random sequence which satisfies uniform distribution, zero cocorrelation and ideal nonlinearity to achieve higher level of security. The proposed scheme is resistant to the known attacks. Theoretic and numerical simulation analyses indicate that our scheme is efficient and satisfies high security.