title: masking a UIImage
body: <p>I'm working on an app that can change the borders or a rectangular UIImage. The borders will vary, but will look like the UIImage was cut out with scissors, or something to that affect.</p>
  
  <p>What is the best way to do this?</p>
  
  <p>My first thought is to prep a bunch of transparent PNGs with the correct border effect I'm looking for, and then somehow use that as a mask for my UIImage. Is this the right path? Or is there a more flexible programmatic way to do this?</p>