fembooru/ext/qr_code/main.php

<?php declare(strict_types=1);

class QRImage extends Extension
{
    /** @var QRImageTheme */
    protected $theme;

    public function onDisplayingImage(DisplayingImageEvent $event)
    {
        $this->theme->links_block(make_http(make_link('image/'.$event->image->id.'.'.$event->image->ext)));
    }
}