http://stackoverflow.com/questions/13153223/how-to-crop-the-image-using-uibezierpath
http://iosdevelopertips.com/cocoa/how-to-mask-an-image.html
http://stackoverflow.com/questions/12670051/iphone-uibezierpath-irregular-image-cropping
http://blog.devedup.com/index.php/2010/03/03/iphone-animate-an-object-along-a-path/