$data = file_get_contents('testn.html');

$res = [];

if(preg_match_all('/<\s*img[^>]+>/', $data, $matches)){

    $pattern = '([\'"])(.*?)\1';

    $attributes = ['src', 'alt', 'title'];

    foreach ($matches[0] as $key => $item){

        foreach ($attributes as $name)
            $res[$key][$name] = preg_match('/'. $name .'\s*=\s*'. $pattern .'/i', $item, $m) ? $m[2] : null;

    }

}