You should use GL_NEAREST for this. Something is not to scale here, either you're drawing the image to small or bigger, or the image is at the wrong resolution, make sure your window client area is the right size, not the window itself, also make sure you're not using mipmap.
And why is the half right of the picture black???
More info on how your drawing it and the size of the window would help too.
: Restored post contents from history.