I had an idea of creating a clip image by using CSS, so the CSS clip property looked like the perfect way to achieve that. After some googling I found Joe's article at seifi.org. Joe advocated an entirely functional, but unnecessarily complex solution. 

I came up with a much simpler way. The trick is that you don't need to use the CSS clip property when you want to clip an image. Here is a simple way to clip an image to 300x200px, push 20px top and 30px left:

div.imageWrapper {
  width: 300px;
  height: 200px;
  overflow: hidden;
}

div.imageWrapper img {
 margin-top: -20px;
 margin-left: -30px;
}