01
Motion blur leaves directional traces that can constrain an inverse estimate. Defocus spreads points in discs, often with a radius that changes across the frame.
02
Pixelation discards within-cell variation. Enlarging a block smoothly can remove the staircase appearance, but it cannot reveal the original values that were averaged away.
03
A censorship mosaic is designed to destroy identity. A model may invent a plausible face or word, but plausibility is not recovery and should never be described as such.
04
Inspect the frequency pattern before choosing a tool. Regular grid peaks favour a block diagnosis; elongated edge echoes favour motion; neither should be treated with ordinary sharpening alone.