Jenssegers\ImageHash\Implementations\AverageHash::hash PHP Method

    public function hash($resource)
    {
        // Resize the image.
        $resized = imagecreatetruecolor(static::SIZE, static::SIZE);
        imagecopyresampled($resized, $resource, 0, 0, 0, 0, static::SIZE, static::SIZE, imagesx($resource), imagesy($resource));
        // Create an array of greyscale pixel values.
        $pixels = [];
        for ($y = 0; $y < static::SIZE; $y++) {
            for ($x = 0; $x < static::SIZE; $x++) {
                $rgb = imagecolorsforindex($resized, imagecolorat($resized, $x, $y));
                $pixels[] = floor(($rgb['red'] + $rgb['green'] + $rgb['blue']) / 3);
            }
        }
        // Free up memory.
        imagedestroy($resized);
        // Get the average pixel value.
        $average = floor(array_sum($pixels) / count($pixels));
        // Each hash bit is set based on whether the current pixels value is above or below the average.
        $hash = 0;
        $one = 1;
        foreach ($pixels as $pixel) {
            if ($pixel > $average) {
                $hash |= $one;
            }
            $one = $one << 1;
        }
        return $hash;
    }