如何在ASP.Net GridView中使用AutoGenerateEditButton的图像而不是文本

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" OnRowEditing="GridView1_RowEditing">
    <Columns>
        <asp:BoundField DataField="Name" HeaderText="Name" />
        <asp:BoundField DataField="Age" HeaderText="Age" />
        <asp:TemplateField HeaderText="Edit">
            <ItemTemplate>
                <asp:ImageButton ID="btnEdit" runat="server" ImageUrl="edit.png" CommandName="Edit" />
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
{
    GridView1.EditIndex = e.NewEditIndex;
    // 执行编辑操作
}