<?php
$arrayTypes = [
    'thumb_',
    'icon_'
];

function getDirContents($dir, &$results = array()){
    $files = scandir($dir);

    foreach($files as $key => $value){
        $path = realpath($dir.DIRECTORY_SEPARATOR.$value);
        if(!is_dir($path)) {
            $results[] = $path;
        } else if($value != "." && $value != "..") {
            getDirContents($path, $results);
            $results[] = $path;
        }
    }

    return $results;
}

$paths = getDirContents($argv[1]);

foreach ($paths as $path) {
    $filename = explode("/", $path);
    $fname = $filename[count($filename) - 1];

    foreach ($arrayTypes as $type) {
        $fname_thumb = $type.$fname;
        $newPath = str_replace($fname, $fname_thumb, $path);
        exec('convert '.$path
            .' -resize 50% '.$newPath);
    }
}