MKMapView Image Overlay Application Example.
This code is the one used on I.ndigo's blog post that can be fully read here:
http://i.ndigo.com.br/2012/05/ios-maps-with-image-overlays/
(portuguese version: http://i.ndigo.com.br/2012/05/imagens-como-overlays-em-um-mapa-no-ios/)