ASP.NET WEB 服务应用程序中gridview如何才能显示图片

<asp:GridView ID="GV_MSG" runat="server" AutoGenerateColumns="False" 
                Width=800px HorizontalAlign="Center" GridLines=None>
              
            <Columns>
             <asp:TemplateField>                               
                                 <ItemTemplate>
                                     <input type="checkbox" name="MSG_ID" value='<%#Eval("MSG_ID") %>' />
                                 </ItemTemplate>
                             </asp:TemplateField>
            <asp:TemplateField >
            <ItemTemplate>
           
           <asp:Image ID="tx" runat="server" ImageUrl=<%#  Eval("user_Photo") %>/><br />
            <asp:Label ID="xm" runat ="server" Text=<%# Eval("user_NiceName")%> /></asp:Label> 
           </ItemTemplate>
                <ItemStyle HorizontalAlign="Center" Width="150px" VerticalAlign="Middle" 
                    Height="200px" />
            </asp:TemplateField>
                        <asp:TemplateField >
                        <ItemTemplate>
                  <b>
                  
                    <%# Eval("MSG_time")%> 
          
                  </b>
                  <hr />
                  <small><i>
                   
                    <%# Eval("MSG_data")%>
                  </small>   
                  </ItemTemplate>                            <ItemStyle Height="200px" />                        </asp:TemplateField>
            </Columns>
                
        </asp:GridView>这里是源码  红色字段的内容就是我绑定图片的数据源，这样的方法我在ASP.NET WEB应用程序的网页中可以正常显示图片内容，用 ASP.NET WEB 服务应用程序的网页却显示不出图片