larave 图片上传展示浏览器报 500 错误？

           <tr>
                <th>缩略图：</th>
                <td>
                    <input type="text" size="50" name="art_thumb">
                    <input id="file_upload" name="file_upload" type="file" multiple="true">
                    <script src="{{asset('resources/org/uploadify/jquery.uploadify.min.js')}}" type="text/javascript"></script>
                    <link rel="stylesheet" type="text/css" href="{{asset('resources/org/uploadify/uploadify.css')}}">
                    <script type="text/javascript">
                        <?php $timestamp = time();?>
                        $(function() {
                            $('#file_upload').uploadify({
                                'buttonText' : '图片上传',
                                'formData'     : {
                                    'timestamp' : '<?php echo $timestamp;?>',
                                    '_token'     : "{{csrf_token()}}"
                                },
                                'swf'      : "{{asset('resources/org/uploadify/uploadify.swf')}}",
                                'uploader' : "{{url('admin/upload')}}",
                                'onUploadSuccess' : function(file, data, response) {
                                    $('input[name=art_thumb]').val(data);
                                    $('#art_thumb_img').attr('src','/'+data);

// alert(data);
}
});
});

                </td>
            </tr>
            <tr>
                <th></th>
                <td>
                    <img src="" alt="" id="art_thumb_img">
                </td>
            </tr>