Testing content aware cropping for SilverStripe Idea is that the automatic cropping will crop the most interesting part of the image

ContentAwareImage.php

<?php

/**
 * ContentAwareImage
 *
 * @author stig
 */
class ContentAwareImage {

	protected static $start_time = 0.0;

	public static function start() {
		self::$start_time = microtime(true);
	}

	public static function mark() {
		$end_time = (microtime(true) - self::$start_time) * 1000;
		return sprintf("%.1fms" ,$end_time);
	}
	
	/**
	 *
	 * @param Imagick $image
	 * @return int
	 */
	protected function area(Imagick $image) {
		$size = $image->getImageGeometry();
		return $size['height'] * $size['width'];
	}

	/**
	 * Calculate the entropy for this image
	 *
	 * @param Imagick $image
	 * @param int $area - the amount of pixels for this image
	 * @return float
	 */
	protected function grayscaleEntropy(Imagick $image) {
		$area = $this->area($image);
		$histogram = $image->getImageHistogram();
		$value = 0.0;

		for($idx = 0; $idx < count($histogram); $idx++) {
			$p = $histogram[$idx]->getColorCount() / $area;
			$value = $value + $p * log($p, 2);
		}

		return -$value;
	}

	/**
	 *
	 * @param type $r
	 * @param type $g
	 * @param type $b
	 * @return type
	 */
	protected function colorEntropy(Imagick $image) {
		$area = $this->area($image);
		$histogram = $image->getImageHistogram();
		$value = 0.0;

		$newHistogram = array();

		for($idx = 0; $idx < count($histogram); $idx++) {
			$colors = $histogram[$idx]->getColor();
			$grey = (($colors['r']*0.299)+($colors['g']*0.587)+($colors['b']*0.114));
			
			if(!isset($result[$grey])) {
				$newHistogram[$grey] = $histogram[$idx]->getColorCount();
			} else {
				$newHistogram[$grey] += $histogram[$idx]->getColorCount();
			}
		}

		foreach($newHistogram as $colorCount) {
			$p = $colorCount / $area;
			$value = $value + $p * log($p, 2);
		}
		
		return -$value;
		
	}

	/**
	 *
	 * @param Imagick $image
	 * @param int $targetHeight
	 * @param int $targetHeight
	 * @param int $sliceSize
	 * @return array
	 */
	protected function getAdaptiveOffset(Imagick $image, $targetWidth, $targetHeight) {
		$size = $image->getImageGeometry();
		$originalWidth = $scanWidth = $size['width'];
		$originalHeight = $scanHeight = $size['height'];
		$goalY = $goalX = 0;

		$sliceSize = ceil($this->area($image) / (1024 * 2));

		$firstImage = $otherImage = null;

		while($scanHeight-$goalY > $targetHeight) {
			$slizeSize = min(array($scanHeight - $goalY - $targetHeight, $sliceSize));
			if(!$firstImage) {
				$firstImage = clone($image);
				$firstImage->cropImage($originalWidth, $slizeSize, 0, $goalY);
			}
			if(!$otherImage) {
				$otherImage = clone($image);
				$otherImage->cropImage($originalWidth, $slizeSize, 0, $scanHeight - $slizeSize);
			}
			if($this->grayscaleEntropy($firstImage) < $this->grayscaleEntropy($otherImage)) {
				$goalY += $slizeSize; $firstImage = null;
			} else {
				$scanHeight -= $slizeSize; $otherImage = null;
			}
		}

		$firstImage = $otherImage = null;

		while($scanWidth-$goalX > $targetWidth) {
			$sliceSize = min(array(($scanWidth-$goalX-$targetWidth), $sliceSize));
			if(!$firstImage) {
				$firstImage = clone($image);
				$firstImage->cropImage($sliceSize, $originalHeight, $goalX, 0);
			}
			if(!$otherImage) {
				$otherImage = clone($image);
				$otherImage->cropImage($sliceSize, $originalHeight, $scanWidth - $sliceSize, 0);
			}
			// $firstImage has more entropy, so keep $otherImage
			if($this->grayscaleEntropy($firstImage) < $this->grayscaleEntropy($otherImage)) {
				$goalX += $sliceSize; $firstImage = null;
			} else {
				$scanWidth -= $sliceSize; $otherImage = null;
			}
		}

		return array('x' => $goalX, 'y' => $goalY);
	}

	/**
	 *
	 * @param Imagick $original
	 * @param int $targetWidth
	 * @param int $targetHeight
	 * @return array
	 */
	protected function getOffset(Imagick $original, $targetWidth, $targetHeight) {

		$image = clone($original);

		// Enhance edges within the image
		#$image->edgeimage($radius = 1);
		// Turn image into a grayscale
		#$image->modulateImage(100, 0, 100);
		// Force all pixels below this to be totally black
		#$image->blackThresholdImage("#0f0f0f");

			// Turn image into a grayscale
		$image->modulateImage(100, 0, 100);
		// Force all pixels below this to be totally black
		$image->modulateImage(100, 0, 100);
		#$image->blackThresholdImage("#000000");
		$image->whitethresholdimage("#9f9f9f");
		$image->edgeimage($radius = 1);

		#$original->modulateImage(100, 0, 100);
		
		#$original->blackThresholdImage("#5f5f5f");
		#$original->whitethresholdimage("#9f9f9f");
		#$original->contrastStretchImage(0,1);
		#$original->edgeimage($radius = 0.5);

		return $this->getAdaptiveOffset($image, $targetWidth, $targetHeight);
	}

	/**
	 *
	 * @param Imagick $image
	 * @param int $targetWidth
	 * @param int $targetHeight
	 * @return array
	 */
	protected function getMiddleOffset($image, $targetWidth, $targetHeight) {
		$size = $image->getImageGeometry();
		$originalWidth = $size['width'];
		$originalHeight = $size['height'];
		$goalX = (int)(($originalWidth-$targetWidth)/2);
		$goalY = (int)(($originalHeight-$targetHeight)/2);
		return array('x' => $goalX, 'y' => $goalY);
	}



	/**
	 *
	 * @param Imagick $image
	 * @param int $targetWidth
	 * @param int $targetHeight
	 * @return array
	 */
	protected function getOutsideCropSize(Imagick $image, $targetWidth, $targetHeight) {
		$source = $image->getImageGeometry();
		if(($source['width'] / $source['height']) < ($targetWidth / $targetHeight)) {
			$scale = $source['width'] / $targetWidth;
		} else {
			$scale = $source['height'] / $targetHeight;
		}
		return array('width' => (int) ($source['width'] / $scale), 'height' => (int) ($source['height'] / $scale));
	}

	/**
	 *
	 * @param string $imagePath
	 * @param int $targetWidth
	 * @param int $targetHeight
	 * @return boolean|\Imagick
	 */
	public function crop($imagePath, $targetWidth, $targetHeight) {
		try {
			$image = new Imagick($imagePath);
		} catch(ImagickException $e) {
			return false;
		}
		
		// First get the size that we can use to safely trim down the image to
		// without cropping any sides
		$crop = $this->getOutsideCropSize($image, $targetWidth, $targetHeight);
		$image->resizeImage($crop['width'], $crop['height'], Imagick::FILTER_CATROM, 0.5);

		// Get the offset for cropping the image further
		#$offset = $this->getOffset($image, $targetWidth, $targetHeight);
		$offset = $this->getMiddleOffset($image, $targetWidth, $targetHeight);
		$image->cropImage($targetWidth, $targetHeight, $offset['x'], $offset['y']);

		$image->setImageCompression(imagick::COMPRESSION_JPEG);
		$image->setImageCompressionQuality(75);
		$image->stripImage();
		return $image;
	}
}

RootURLController.php

<?php

class RootURLController extends Controller {

	public function index() {
		$from = ASSETS_PATH.'/real/';
		$to = ASSETS_PATH.'/thumbs/';

		$files = glob($from.'/*');

		ContentAwareImage::start();
		foreach($files as $file) {
			$fileInfo = pathinfo($file);
			$coolImage = new ContentAwareImage();
			$image = $coolImage->crop($file, 100, 100);
			if(!$image) { continue; }
			$thumbName = $fileInfo['filename']."-cropped.jpg";
			$image->writeImage($to.'/'.$thumbName);
			echo '<img src="'.ASSETS_DIR.'/thumbs/'.$thumbName.'" />';
		}
		echo ContentAwareImage::mark();
	}

}