Jenssegers\ImageHash\Implementations\PerceptualHash::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));
        // Get luma value (YCbCr) from RGB colors and calculate the DCT for each row.
        $matrix = [];
        $row = [];
        $rows = [];
        $col = [];
        $cols = [];
        for ($y = 0; $y < static::SIZE; $y++) {
            for ($x = 0; $x < static::SIZE; $x++) {
                $rgb = imagecolorsforindex($resized, imagecolorat($resized, $x, $y));
                $row[$x] = floor($rgb['red'] * 0.299 + $rgb['green'] * 0.587 + $rgb['blue'] * 0.114);
            }
            $rows[$y] = $this->DCT1D($row);
        }
        // Free up memory.
        imagedestroy($resized);
        // Calculate the DCT for each column.
        for ($x = 0; $x < static::SIZE; $x++) {
            for ($y = 0; $y < static::SIZE; $y++) {
                $col[$y] = $rows[$y][$x];
            }
            $matrix[$x] = $this->DCT1D($col);
        }
        // Extract the top 8x8 pixels.
        $pixels = [];
        for ($y = 0; $y < 8; $y++) {
            for ($x = 0; $x < 8; $x++) {
                $pixels[] = $matrix[$y][$x];
            }
        }
        // Calculate the median.
        $median = $this->median($pixels);
        // Calculate hash.
        $hash = 0;
        $one = 1;
        foreach ($pixels as $pixel) {
            if ($pixel > $median) {
                $hash |= $one;
            }
            $one = $one << 1;
        }
        return $hash;
    }