<script>  
    $(document).ready(function() {  
        $('#submit-button').click(function() {  
            var imgmg = $('#imgmg')[0];  
            var imgsh = $('#imgsh')[0];  
            var imgwd = $('#imgwd')[0];  
            var formData = new FormData();  

            formData.append('imgmg', imgmg.files[0]);  
            formData.append('imgsh', imgsh.files[0]);  
            formData.append('imgwd', imgwd.files[0]);  
  
            $.ajax({  
                url: "{:url('index/ajax_img')}",  
                type: 'POST',  
                data: formData,  
                cache: false,  
                contentType: false,  
                processData: false,  

                beforeSend: function(){
                    $('#tonerInfowarning').text('正在提交，请勿继续操作...');
                },

                error: function(result) {  
                    alert('提交照片格式出错，请重新扫码');
                }, 
                success: function(result) {  
                    if (result == '提交成功') {window.location.href = '{:url("index/result_ok")}';}else{
                       alert(result); 
                    }
                }  
            });  
        });  
    });  
</script>

beforeSend: function()加入ajax中，这是一个回调函数