title: Difference between UIButton methods that set image
body: <p>Please tell me what's the difference between two UIButton methods:</p>
  
  <pre><code>- (void)setBackgroundImage:(UIImage *)image forState:(UIControlState)state
  </code></pre>
  
  <p>and</p>
  
  <pre><code>- (void)setImage:(UIImage *)image forState:(UIControlState)state
  </code></pre>
  
  <p>Apple documentation says nothing about it.</p>