title: iPhone: Mask UIImageView of differing dimensions into square dimension
body: <p>I have a bunch of UIImageViews that are in different proportions.  Some of 100x101 some are 130x121.</p>
  
  <p>How can I mask these to 80x80 and NOT stretch the images?  I basically just want to mask a square out of each one.  (kind of like the Apple's Photo thumbnail view does)</p>