I have a samsung Galaxy a51, when I take pictures using the back camera (and when in low light conditions or even covering the camera completely) it shows some sort of smudge on the top left corner (some sort of noise smudge). Image attached. it is super visible when taking the picture. Any ideas of what could it be? I've had the phone for 2 months now.
Have you tried clearing the cache and data on the camera app?
Navigate to your settings > apps > click on the 3 dots in the top right corner > select "Show System Apps" > find and click on Camera > storage clear cache and data.
Also, the picture you previously provided, I'm not able to make out the symptom you are experiencing. Can you please provide another picture so I can assist you better?
Have you tried seeing if you still experience the same thing using a third-party app that uses the camera?