Change the image's origin of map annotation view?

Question

The regular annotation pin's origin is in the middle of the bottom so, the pin always point to the same place.

But when I add my custom image, its origin is the center of the image, so every zoom in or out, the bottom of my image point to a different place.

Here my pin is supposed to point to the center of paris BUT

but when I zoom in, the bottom of my pin isn't pointing to the center of Paris.

I'm trying with the CGRect.origin but didn't get anything useful.

Here is my code:

- (MKAnnotationView *)mapView:(MKMapView *)theMapView viewForAnnotation:(id <MKAnnotation>)annotation
{
    MKAnnotationView * customPinView = [[MKAnnotationView alloc] init];
    UIImage * img = [UIImage imageNamed:@"waterPin.png"] ;
    CGRect resizeRect;
    resizeRect.size.height = 40;
    resizeRect.size.width = 40;
    resizeRect.origin = (CGPoint){0.0f, 0.0f};
    UIGraphicsBeginImageContext(resizeRect.size);
    [img drawInRect:resizeRect];
    UIImage *resizedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    customPinView.image = resizedImage;
    return customPinView;
}