Check if image file ??

allow_url_fopen is activated in your PHP config 

 $filename = "http://".$_SERVER['SERVER_NAME']."

/media/img/".$row['CatNaam'].".jpg";
 echo"  <img src=\"".$filename."\" alt=\"".$row['CatNaam']."\">";

        

        if (file_exists($filename)) {
            echo "The file $filename exists";
        } else {
            echo "The file $filename does not exist";
        }