readfile（）有时无法处理图像

Question

I have a function to read file. I want to show images while download other file types. but I am getting bulky codes while trying to view image. Below is my code:

public function download($file_name=NULL){
    if($file_name == NULL):
    $file_name = $this->uri->segment('3');
    endif;

    $tr= explode(".", $file_name);
    $array = array("JPG", "JPEG", "jpg", "jpeg", "PNG", 
"png", "GIF", "gif", "tiff", "TIFF");
    if(!in_array($tr[1], $array)):
    header('Content-Disposition: attachment; filename="'.$file_name.'"');
    else:
    readfile(BASEPATH.'../assets/images/upload/'.$file_name);
    endif;
}

And I am trying to view image using:

<img class="pull-left" src="'.$this->download($img).'" /> <!-- This is image1.jpg -->

I am getting these type of non readable codes:

�r��g��7�hi99 c�Zi�zZ����ԕ�jXn⸑�7V+�56���6��qN�(�Ub��9���>tba�,� ߕs־'K�uY��a�S��ۜ�u�b�&���Z�=�]�i���
=n�I&I�#<�{dw� mgO}a���f�h�"����+����m��n%��Mnf�

Please help me to find the issue.