private function getImageFiles()
    {
        if ($this->imageFiles === null) {
            // Get a list of images.
            $this->imageFiles = $this->filesystem
                ->find()
                ->in('files://')
                ->name('/\.jpe?g$/')
                ->name('*.png')
                ->toArray()
            ;
        }

        return $this->imageFiles;
    }