An image processing system includes an image processing apparatus and a decryption server interconnected via a network. When a portable recording medium having an encrypted target file and access information to access a decryption server that decrypts this encrypted target file, recorded therein, is connected to a connector of an image processing apparatus, the image processing apparatus reads out the encrypted target file and the access information from the portable recording medium connected thereto, accesses the decryption server according to the access information, then transmits the encrypted target file to the decryption server. The decryption server decrypts the encrypted target file received therefrom, and returns it to the image processing apparatus. The image processing apparatus executes processing on the decrypted target file that is returned therefrom.