Load a QGIS-Server WMS-Layer to OpenLayers3 with manually created GetLegendGraphic image

HTML

<script src="http://openlayers.org/en/v3.1.1/build/ol.js"></script>
Load a QGIS-Server-WMS-Layer to OpenLayer3
<div id="map">
  
  <div id="legende">
     <h2>Legend:</h2>

    <div class="udiv_legende" id="legende_1">
        <img src="http://qgiscloud.com/expedio/wfs_t/wms?Service=WMS&REQUEST=GetLegendGraphic&VERSION=1.0.0&FORMAT=image/png&WIDTH=12&HEIGHT=12&LAYER=buffer">
        <br>
        <br>
    </div>
</div>
  
</div>

CSS

#map {
    height: 256px;
    width: 512px;
    border:1px solid black;
}

JavaScript

var map = new ol.Map({
     target: 'map',
     renderer: 'canvas',
     layers: [
     new ol.layer.Tile({
         source: new ol.source.OSM()
     }),

     new ol.layer.Image({
         source: new ol.source.ImageWMS({
             url: 'http://qgiscloud.com/expedio/wfs_t/wms?',
             ratio: 1,
             params: {
                 'LAYERS': 'buffer, buffer_new',
                     'TRANSPARENT': 'true'
             }
         })
     })

     ],
     view: new ol.View({
         projection: 'EPSG:3857',
         center: [-8238683.374712203, 4998174.938711717],
         zoom: 15

     })
 });