Well, a Sprite doesn't really have a corner. If you mean a bounding box for an Object based on the Sprite, then you want to center the box around (0,0) (assuming the Object will be positioned at (0,0)). Something like:
<p>width = sprite -> getWidth()
<p>height = sprite -> getHeight()
<p>corner x = -1 * width / 2
<p>corner y = -1 * height / 2