Calculates average image hash, or compares two images if given two image paths. Ported code from example at https://01101001.net/averagehash.php

averagehash.php

<?php

$hash1 = "";
$hash2 = "";
$similarity = 0;

if (isset($argv[1])) {
  $hash1 = averageHash($argv[1]);
}
if (isset($argv[2])) {
  $hash2 = averageHash($argv[2]);
}
if (!empty($hash1) && !empty($hash2)) {
  // Return similarity in percent
  $similarity = compareHash($hash1, $hash2);
  echo $similarity;
  die;
}
if (!empty($hash1)) {
  // Return single image hash
  echo $hash1;
  die;
}

function averageHash($imagePath)
{

  $image = null;
  $extension = pathinfo($imagePath, PATHINFO_EXTENSION);

  switch ($extension) {
    case 'jpg':
    case 'jpeg':
      // For JPEG images
      $image = imagecreatefromjpeg($imagePath);
      break;
    case 'png':
      // For PNG images
      $image = imagecreatefrompng($imagePath);
      break;
    case 'gif':
      // For GIF images
      $image = imagecreatefromgif($imagePath);
      break;
    default:
      echo "$imagePath: This script only works with png,jpg or gif images. Exiting.";
      break;
  }

  if (is_null($image)) {
    return null;
  }

  $hashImage = imagescale($image, 8, 8);
  imagefilter($hashImage, IMG_FILTER_GRAYSCALE);

  $averagePixel = 0;
  $averageHashValue = "";

  // Calculate the average brightness of the pixels.
  for ($y = 0; $y < 8; $y++) {
    for ($x = 0; $x < 8; $x++) {
      $averagePixel += imagecolorat($hashImage, $x, $y);
    }
  }
  $averagePixel /= 64.0;

  // Go through the image pixel by pixel.
  // Return 1-bits when a pixel is equal to or brighter than the average
  // pixel, and 0-bits when it's below.
  for ($y = 0; $y < 8; $y++) {
    for ($x = 0; $x < 8; $x++) {
      if (imagecolorat($hashImage, $x, $y) >= $averagePixel) {
        $averageHashValue .= "1";
      } else {
        $averageHashValue .= "0";
      }
    }
  }

  $hashValue = dechex((int) bindec($averageHashValue));

  return $hashValue;
}

function xorCompare($bigInt1, $bigInt2)
{
  while (strlen($bigInt1) < strlen($bigInt2)) {
    $bigInt1 = "0" . $bigInt1;
  }
  while (strlen($bigInt2) < strlen($bigInt1)) {
    $bigInt2 = "0" . $bigInt2;
  }

  $onexortwo = "";
  for ($i = 0; $i < strlen($bigInt1); $i++) {
    if ($bigInt1[$i] == $bigInt2[$i]) {
      $onexortwo .= "0";
    } else {
      $onexortwo .= "1";
    }
  }

  return $onexortwo;
}

function compareHash($hash1, $hash2)
{
  return (64 - (count(explode("1", xorCompare($hash1, $hash2))) - 1)) * 100.0 / 64.0;
}