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 bio-chaotic 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.