function checkedRadioBtn(){

    var newL;
if(document.getElementById("bild-switch_1").checked){

        newL = new ol.layer.Image({
             source: new ol.source.ImageStatic({
                url: 'Bild1.png', 
                imageSize: [122, 44],
                projection: proj,
                imageExtent: proj.getExtent()
            })
        });
        
    }else if(document.getElementById("bild-switch_2").checked){

        newL = new ol.layer.Image({
             source: new ol.source.ImageStatic({
                url: 'Bild2.png', 
                imageSize: [722, 154],
                projection: proj,
                imageExtent: proj.getExtent()
            })
        });
     ...
 map.removeLayer(baseLayer);
     map.addLayer(newL);
};