An Active Attack is a type of steganography attack in which the attacker changes the carrier during the communication process. Which of the following techniques is used for smoothing the transition…

Soften applies a mild, generalized smoothing across the image and does not specifically target or control the contrast at hard edges where significant color transitions occur.

Rotate is a geometric transformation that changes the angular orientation of the entire image and has no effect on smoothing color transitions or reducing edge contrast.

Sharpen increases the contrast and accentuates edge detail, which is the opposite of smoothing transitions - it would make hard color boundaries more visible, not less.

Blur works by averaging neighboring pixel values across a region, which directly softens sharp boundaries and reduces the high-frequency contrast at hard edges where significant color transitions exist. In the context of a steganography active attack, blurring the carrier image after altering it helps conceal the modifications by making abrupt color changes appear gradual and natural. This targets exactly the artifact type - hard edge discontinuities - that would most likely betray hidden content.