Victor wants to send an encrypted message to his friend. He is using certain steganography technique to accomplish this task. He takes a cover object and changes it accordingly to hide information…

In the distortion technique, the sender encodes the message by introducing controlled distortions into an existing cover object such as an image or audio file. Recovery depends entirely on the receiver having access to the original cover and comparing it with the received version to extract the differences - which is the exact behavior described in the question.

The spread spectrum technique disperses hidden data across a wide frequency range of the carrier signal rather than modifying a discrete cover and requiring original-comparison for decoding.

The cover generation technique constructs a brand-new cover object purpose-built to carry the secret message rather than altering an existing one.

The substitution technique replaces least-significant bits or redundant portions of the cover with secret data and does not rely on comparison with an original cover for recovery.