Compare.php

<?php
namespace Foo9\Img;

use Symfony\Component\Process\Process;
use Symfony\Component\Process\ProcessBuilder;

class Compare
{
	/** @var integer */
	private $fuzz;

	/** @var integer */
	private $timeout;

	/**
	 * 
	 * 
	 * @param integer $fuzz
	 * @param integer $timeout
	 */
	public function __construct($fuzz, $timeout = 3600)
	{
		$this->fuzz = $fuzz;
		$this->timeout = $timeout;
	}

	/**
	 * 
	 * 
	 * @param string $base
	 * @param string $compare
	 * @param string $output
	 * 
	 * @throws RuntimeException
	 * 
	 * @return integer
	 */
	public function run($base, $compare, $output)
	{
		$cmdline = self::createCmdline($this->fuzz, $base, $compare, $output);

		$process = new Process($cmdline);
		$process->setTimeout($this->timeout);
		$process->run();

		// @see http://www.imagemagick.org/script/compare.php
		// The compare program returns 2 on error otherwise 0
		// if the images are similar or 1 if they are dissimilar.
		$exitCode = $process->getExitCode();
		switch ($exitCode) {
			case 0:
			case 1:
				$diffPixels = $process->getErrorOutput();
				break;
			case 2:
			default:
				throw new \RuntimeException($process->getErrorOutput());
		}

		$size = getimagesize($output);
		$allPixels = $size[0] * $size[1];

		return round(($diffPixels / $allPixels) * 100);
	}

	/**
	 * 
	 * 
	 * @param integer $fuzz
	 * @param string $base
	 * @param string $compare
	 * @param string $output
	 * 
	 * @return string
	 */
	public static function createCmdline($fuzz, $base, $compare, $output)
	{
		$arguments = ProcessBuilder::create(array(
			$base,
			$compare,
			$output
		))
		->getProcess()
		->getCommandLine();

		return implode(' ', array(
			'/usr/local/bin/compare',
			'-dissimilarity-threshold 1',
			'-fuzz ' . (int) $fuzz . '%',
			'-metric AE',
			'-highlight-color blue',
			$arguments
		));
	}
}

Crop.php

<?php
namespace Foo9\Img;

use Symfony\Component\Process\Process;
use Symfony\Component\Process\ProcessBuilder;

class Crop
{
	/** @var integer */
	private $timeout;

	/**
	 * 
	 * 
	 * @param integer $timeout
	 */
	public function __construct($timeout = 3600)
	{
		$this->timeout = $timeout;
	}

	/**
	 * 
	 * 
	 * @param string $base
	 * @param string $compare
	 * @param string $output
	 * 
	 * @throws RuntimeException
	 * 
	 * @return void
	 */
	public function run($base, $compare)
	{
		$cmdline = self::createCmdline($base, $compare);

		$process = new Process($cmdline);
		$process->setTimeout($this->timeout);
		$process->run();
		if (!$process->isSuccessful()) {
			throw new \RuntimeException($process->getErrorOutput());
		}
	}

	/**
	 * 
	 * 
	 * @param string $base
	 * @param string $compare
	 * 
	 * @return string
	 */
	public static function createCmdline($base, $compare)
	{
		list($width, $baseHeight) = getimagesize($base);
		$compareHeight = getimagesize($compare)[1];
		
		if ($baseHeight > $compareHeight) {
			$imageToCrop = $compare;
			$heightToCropTo = $baseHeight;
		} else {
			$imageToCrop = $base;
			$heightToCropTo = $compareHeight;
		}

		$crop = ProcessBuilder::create(array(
			$imageToCrop
		))
		->getProcess()
		->getCommandLine();

		return implode(' ', array(
			'/usr/local/bin/convert',
			"${crop}",
			'-background none',
			"-extent ${width}x${heightToCropTo}",
			"${crop}"
		));
	}
}