Dark dots or thin marks that show up most on bright, even areas usually point to dust or debris somewhere in the optical path, most often on the sensor. In video, this can become more noticeable on flat bright backgrounds like white paper.

Things to check:

• Clean the front and rear of the lens first.
• If the marks stay in the same place in the frame across different shots/lenses, the sensor likely needs cleaning.
• Use the camera’s sensor-cleaning function if available, then test again.
• If needed, have the sensor professionally cleaned.

Also consider exposure/focus artifacts: very high ISO noise, compression, or moiré/aliasing can create odd-looking patterns, but those usually change with scene detail and don’t stay fixed in one spot.

A simple test: film a plain bright wall or white paper, then change lenses. If the marks remain in the same position, it’s probably sensor dust/debris rather than a lens problem.