Security is a continuous process of protecting the resources of a computer system from hackers or attackers. Multimedia comes in the form of text, image, audio and video, and all are very important modes of communication that gives users more ways to express their feelings. In traditional cryptography, encipherment and decipherment take more processing time to secure bulky data with a high order of complexity in data storage, as well as in the transmission of multimedia-oriented applications. Therefore, selective encryption reduces computational costs, overhead and size of data in the encipherment process, which is always advantageous for all the parties involved in communication. In this paper, we propose a region-based selective image encryption to secure information in an efficient manner to achieve reduced encryption time. Secrecy of unnecessary information within an image is not required for both the ends in communication. Here, security summarised as aggregated chaos-based coding with most significant bit diffusion and recentness keyless substitution cipher at the pixel level on the ROI image obtained by a hybrid region growing method. This technique significantly reduces the storage space and transmission costs. Experimental results confirm it is a more secure and fast encryption method for large sized images.