On the CodeGeekz site there's a new post showing you how to use the Imagick extension and a custom library to crop images based on their entropy (keeping the "busiest" part of the image).

The need to resize and crop images in order to create thumbs, is a very common scenario for most websites. For example a blog like this one uses images in the content of the posts, images which at some point are used to create a thumb for the homepage. In most cases, the thumb’s dimensions are not dynamic but are static throughout the website in order to better fit the template. This however creates a major problem when we try to automatically resize and crop our images in the desired dimensions.

He starts with an example of the normal kind of cropping based on a given height and width. He points out an issue with "smart cropping" and resizing the image with the cropping is done. Instead, he's made use of Imagick in his library to produce a better cropped image based on the parts of the image with the most entropy.