title: cocos2d content.size, boundingBox and size
body: <p>im writing a game to find the differences between 2 images. i created a subclass of CCSprite, Spot. firstly i tried to create small images and add itself according to it's position, but later i found the position is hard to determine, since it's hard to avoid offset of 1 or 2 pixels. </p>
  
  <p>then i tried to make the Spot the same size as the image, with the other part transparent. but I still need to find out the 'hotspot' of finger tap. but when i use CGRectContainsPoint([self boundingBox], touchLocation), it's actually the whole image. </p>
  
  <p>so is there any other way to do this? like content.size or self.size, and make a CGRect out of it's non-transparent part? 
  Thank you. </p>