My com is Inspirion 1720.

Today, I found a tiny black line with 3 or 4 mm length on my screen

At first, I thought it was a small hair or debris, but it was not.

Usually, missing pixel has light without color.

However, it's black and very noticible when I set my background with a bright color, (white, yellow, pink, light green, etc.)

What is this?