<?php

$config = [
    'square' => '200x200',
    'normal' => '400x400:fit',
    'big'    => '1280x720:fit,quality=100',
];

$result = (new kartinki\Kartinki\Thumbnailer)->createThumbnails(
    '/path/to/image/filename.jpg',
    $config,
    '/output/dir' // optional
);

<?php
$result->getThumbnails();
// [
//     'square' => '1ceebb2cf4b0425a0ea1e1cb49810a07_square.jpg',
//     'normal' => '1ceebb2cf4b0425a0ea1e1cb49810a07_normal.jpg',
//     'big'    => '1ceebb2cf4b0425a0ea1e1cb49810a07_big.jpg'
// ]
 
$result->getUniqueId();
// '1ceebb2cf4b0425a0ea1e1cb49810a07'

$result->getExtension();
// 'jpg'