Conventional cryptography uses encryption key, which are long bit strings and are very hard to memorize such a long random numbers. Also it can be easily attacked by using the brute force search or technique. Instead of traditional cryptography, biometric e.g. fingerprint, iris, face, voice etc uniquely identifies a person and a secure method for stream cipher, because Biometric characteristics are ever living and unstable in nature (with respect to recognition). In this paper we used the idea of biochaotic stream cipher which encrypts the images over the electronic media by using a biometric key and a bio-chaotic function. It enhances the security of the images and it should not be compromised. The idea also gives birth to a new kind of stream cipher named bio-chaotic stream cipher. The paper also describes how to generate a key from a biometric string and how to encrypt and decrypt the desired data by using the bio-chaotic function.