The PHP readdir() function returns the name of the next entry in a directory.

<?php
$dir = '/images/';

// open a directory and read its contents
if (is_dir($dir)) {
    if ($dh = opendir($dir)){
        while (($file = readdir($dh)) !== false) {
            echo 'filename:' . $file . '<br>';
        }
        closedir($dh);
    }
}
?>

filename: image1.jpg
filename: image2.jpg
filename: logo.png

readdir(dir)