Customize shortcode function for inserting an image

Hello!

I am trying to customize a given function for shortcode about a banner. The banner contains a title and a subtitle.But I want to add an image left to the title. the function is like this:

function banner($atts,$content=null){
    ob_start();
extract(shortcode_atts(array("title" => '', 'subtitle'=>'', 'type'=> ''), $atts));

    if($type == 2){
	   return '<div id="banner" class="banner-2">
            <div class="site-slogan">
                <div class="slogan-inner clearfix">
                    <h2>'.$title.'</h2>
                    <h2>'.$subtitle.'</h2>
                </div>
            </div>
        </div>';
    }

I want to insert <img src=”…”> so when I want to edit the section(it’s one page parallax theme)i will be able to add/change an image dynamically.
I tried <img src=’.$content.’> but it’s not working. Should I add another variable(image) to the function like title and subtitle? of cource i have to customize and the css file properly. but all i see in my page is a broken image, which means that it doesn’t take the parameter value!

I hope someone could help me!