struts上传

我上传的时候为什么图片上传不了呢？

<interceptor-ref name="fileUpload">
         <param name="maximumSize">4096000</param>
         <param name="allowedTypes">image/bmp,image/png,image/gif,image/jpeg,image/jpg,application/msword,application/vnd.ms-excel</param> 
          </interceptor-ref>
          <interceptor-ref name="defaultStack"></interceptor-ref>


excel和word文件都能上传  为什么就图片上传不了呢