GD Difference Hash for jenssegers / imagehash package (around 4x quicker than Intervention)

GdDifferenceHash.php

<?php

namespace App\Image;

use Jenssegers\ImageHash\Hash;
use Jenssegers\ImageHash\Implementation;

class GdDifferenceHash implements Implementation
{
	/**
	 * @var int
	 */
	protected $size;

	/**
	 * @param int $size
	 */
	public function __construct($size = 8)
	{
		$this->size = $size;
	}

	/**
	 * @inheritdoc
	 */
	public function hash($image)
	{
		$source = imagecreatefromjpeg($image);

		// For this implementation we create a 8x9 image.
		$width = $this->size + 1;
		$height = $this->size;

		// Resize the image.
		// $resized = $image->resize($width, $height);
		$resized = imagecreatetruecolor($width, $height);

		list($origwidth, $origheight) = getimagesize($image);
		imagecopyresized($resized, $source, 0, 0, 0, 0, $width, $height, $origwidth, $origheight);

		$bits = [];
		for ($y = 0; $y < $height; $y++) {
			// Get the pixel value for the leftmost pixel.
			$rgb = $this->pickColor($resized, 0, $y);
			$left = (int) floor(($rgb[0] * 0.299) + ($rgb[1] * 0.587) + ($rgb[2] * 0.114));

			for ($x = 1; $x < $width; $x++) {
				// Get the pixel value for each pixel starting from position 1.
				$rgb = $this->pickColor($resized, $x, $y);
				$right = (int) floor(($rgb[0] * 0.299) + ($rgb[1] * 0.587) + ($rgb[2] * 0.114));

				// Each hash bit is set based on whether the left pixel is brighter than the right pixel.
				// http://www.hackerfactor.com/blog/index.php?/archives/529-Kind-of-Like-That.html
				$bits[] = (int) ($left > $right);

				// Prepare the next loop.
				$left = $right;
			}
		}

		return Hash::fromBits($bits);
	}

	protected function pickColor($image, $x, $y)
	{
		$colorIndex = imagecolorsforindex($image, imagecolorat($image, $x, $y));

		return [$colorIndex['red'], $colorIndex['green'], $colorIndex['blue']];
	}
}

Disclaimer: I haven't thouroughly tested it, so you may want to double check its coming back with the same values as the current implementation.

Note: the package currently requires Imagick due to the interface, so in itself the above code won't be "plug and play" - will likely need to fork the package and adjust the interface to remove that typehint.