I think the best way to identify a dead pixel is to open up an app I have called "Draw". It's a basic drawing app, probably any of them would work. The idea is that it's got a purely white background.
If you think you've identified a dead pixel, draw over the pixel with a blue brush, see if the pixel remains black and you can see it through the blue. It's hard to describe, but a dead pixel will be black against the white background, and then black also after you color over it with a different color.
On my iPad the Apple store was able to identify a number of dead pixels and also an imperfection in the glass. The imperfection in the glass was different in that it looked like a dead pixel, but when you changed the viewing angle it would appear to float on top of the actual screen.
They replaced mine because of the amount of dead pixels and imperfections, but they explained that a certain amount of dead pixels is technically acceptable. I believe he said up to 3 is technically 'okay', by their standards.