similar.php

<?php

    # Algorithm found here: http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html

    $filename = 'image.jpg';

    list($width, $height) = getimagesize($filename);

    $img = imagecreatefromjpeg($filename);
    $new_img = imagecreatetruecolor(8, 8);

    imagecopyresampled($new_img, $img, 0, 0, 0, 0, 8, 8, $width, $height);
    imagefilter($new_img, IMG_FILTER_GRAYSCALE);

    $colors = array();
    $sum = 0;
    
    for ($i = 0; $i < 8; $i++) {
        for ($j = 0; $j < 8; $j++) {
            $color = imagecolorat($new_img, $i, $j) & 0xff;
            $sum += $color;
            $colors[] = $color;
        }
    }

    $avg = $sum / 64;

    $hash = '';
    $curr = '';
    $count = 0;
    foreach ($colors as $color) {
        if ($color > $avg) {
            $curr .= '1';
        } else {
            $curr .= '0';
        }
        $count++;

        if (!($count % 4)) {
            $hash .= dechex(bindec($curr));
            $curr = '';
        }
    }

    print $hash . "\n";