<img src="<?= $this->url('application', ['action'=>'file'],
                            ['query'=>['name'=>$foto], 'thumbnail'=>true]); ?>" alt="" class="d-block w-100" data-toggle="modal" data-target="#exampleModal">

$result .= '<img src="'.('application', ['action'=>'file'],
                            ['query'=>['name'=>$escapeHtml($foto)],  'thumbnail'=>true]).'" alt="" class="d-block w-100" data-toggle="modal" data-target="#exampleModal">';

$this->url