Train a point rather than a bounding box for object detection
Ususally the x,y coordinates of the top-left corner of the bounding box and the width and height of the bounding box is returned by objection detection algorithms (eg: Haar Cascades)
You can always convert a bounding box to a point via the equation:

$BoundingBoxCenter_{x}= \frac{BoundingBoxCorner_{x} +
 BoundingBoxWidth}{2}$
$BoundingBoxCenter_{y}=
 \frac{BoundingBoxCorner_{y} + BoundingBoxHeight}{2}$