The attacker performs probability analysis to test whether the stego object and original data are the same or not.

• A. Stego-only Attack
• B. Chosen-stego Attack
• C. Chi-square Attack
• D. Distinguishing Statistical attack

Answer: (B)

This scenario centers on an attacker who can craft or select stego objects to probe how embedding behaves and to estimate the likelihood that the stego carries a given payload. Being able to choose or create specific stego samples lets the attacker apply probability analysis to test whether the stego object’s embedded data matches the original data. That capability—using controlled, chosen stego inputs to draw statistical conclusions about the relationship between stego and payload—is the hallmark of a chosen-stego attack.

The other approaches describe different aims or access: a chi-square test is a specific statistical method used to spot anomalies in data distributions after embedding; a distinguishing statistical attack tries to tell apart stego from cover rather than verify data equality; and a stego-only attack assumes no access to the original data for comparison.