Recently I discovered that my phone's screen is leaving semi transparent stuck pixels on the edges of the screen , I don't know if it came like that from the previous owner (the phone is used) i just noticed it while using the phone in low brightness , if i set the brightness to 20% or above the pixels are gone , the problem is generally with low brightness and in night , here is a picture to demonstrate it (i made it in photoshop , just to give you an idea about the problem):

thank you

 

should i worry ? , do i need a screen replacement ? or ...you know ... i can just raise the brightness