Techniques pertaining to a security system are disclosed. According to one aspect of the techniques, secured communication of video data between a monitoring system including a monitoring camera and a monitoring terminal is established by encrypting the video data. The monitoring camera is configured to encrypt digital image data before the image data is transmitted to the monitoring terminal. Instead of using commonly used encryption schemes, encryption rules are generated in accordance with an encryption key corresponding to a predetermined encryption algorithm. On the side of the monitoring terminal, decryption rules are generated in accordance with a received description key corresponding to a predetermined decryption algorithm. Depending on implementation, the image data may be encrypted/decrypted line by line, block by block or frame by frame.