Protected Sub GridView1_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles GridView1.RowDataBound
        If e.Row.RowType = DataControlRowType.DataRow Then

            Dim img1 As New Image
            Dim UpdateTime As DateTime

            img1.ImageUrl = "~/images/threeday.gif"


            '显示三天内更新
            If Not Convert.IsDBNull(DataBinder.Eval(e.Row.DataItem, "UpdateTime")) Then
                UpdateTime = DataBinder.Eval(e.Row.DataItem, "UpdateTime")
                Dim ts1 As New TimeSpan(UpdateTime.Ticks)
                Dim ts2 As New TimeSpan(Now.Ticks)
                Dim ts As TimeSpan = ts1.Subtract(ts2).Duration()

                If ts.Days < 3 Then
                    e.Row.Cells(5).Controls.Add(img1)
                End If
            End If
        End If
    End Sub

------解决方案--------------------
你可以这样写数据源：  
select 字段1，字段2，....,DataDiff(day,PostTime,GetDate()) as days  from xxx.....  
这样，你搜索出来的数据源中就多了一个字段days,然后在信息后加个图片，建议用模板页
加上<img src='....' runat="server" visible='<%# Display(Eval("days"))%>'/>

后台CS
public bool Display(string days)
{
   int day=int.parse(days);
   if(day<=3)
      return true;
   else
      return false;
}

------解决方案--------------------

HTML code
<asp:TemplateField>
    <ItemTemplate>
        <b><%# Eval("Title") %></b>
        <asp:Image ID="imgNew" ImageUrl="Images/New.gif" runat="server" Visible='<%# Convert.ToDateTime(Eval("PublicTime")).AddDays(3) > DateTime.Now ? true : false %>'/>
    </ItemTemplate>
</asp:TemplateField>