This is usually caused by flickering indoor lights interacting with your phone’s rolling shutter. Many phone sensors don’t expose the whole frame at once; they scan the image over a short time. If the light source is pulsing in brightness—common with mains-powered lighting—the camera records different brightness levels across the frame, which shows up as dark bands.

The effect depends on the relationship between:

• the light’s flicker rate (often tied to 50/60 Hz power), and
• the camera’s exposure/readout timing.

To reduce it:

• Enable any anti-banding/flicker reduction setting in the camera app.
• Make sure the camera’s power-line frequency is set correctly for your region: 50 Hz or 60 Hz.
• If possible, use shutter speeds/exposure times that are compatible with the local mains frequency.
• Try different lighting or brighter light, which may cause the phone to use a different exposure time.

So the bands are not damage to the camera or paper—they’re a timing mismatch between flickering light and rolling-shutter capture.