jQuery如何验证上传的文件是否为图片

      var path = $("#imgfile").val();
        if (path.length == 0) {
            alert("Please upload the hotel logo!");
            return false;
        } else {
            var extStart = path.lastIndexOf('.'),
                ext = path.substring(extStart, path.length).toUpperCase();
            if (ext !== '.PNG' && ext !== '.JPG' && ext !== '.JPEG' && ext !== '.GIF') {
                alert("Please enter the correct picture format!");
                resetFile();
                return false;
            }
        }