Check if drag / drop content is image

I want to check wether the content dragged/dropped onto an area is an image or not. My Code is working in Chrome and Firefox, but not in Safari. I guess it's because Safari has no dataTransfer type text/html for images. Is there a workaround for Safari?

document.addEventListener( 'drop', function( e ) {      
    var contentHtml;        
    if( e.dataTransfer ){           
        contentHtml = (e.originalEvent || e).dataTransfer.getData('text/html');
        if($(contentHtml).is('img')){
            // do some things, then let the standard drop happen
            return true;
        } else {
            // do other things, prevent drop
            return false;
        }
    }
});