Forms Data Controls :: Make The ImageField Read Only When Changing DetailsView To Insert Mode?

I have some ImageField in my DetailsView and when I changed it to Insert mode then ImageField is also became the textbox that allow you to type something, and my question is how I can make ImageField to be read only when I changed DetailsView to Insert mode?

<asp:DetailsView ID="dvNew" runat="server" AutoGenerateRows="False"
AllowPaging="true" DataKeyNames="ID"
DataSourceID="DataSourceNew" Width="600px" Font-Bold="False" AutoGenerateInsertButton="True" >
<Fields>
<asp:BoundField DataField ="name" SortExpression ="name" HeaderStyle-ForeColor="Black" > </asp:BoundField>
<asp:ImageField DataImageUrlField="Image1Path" NullDisplayText="No Image"
ReadOnly="True" ItemStyle-Height="250" ItemStyle-HorizontalAlign="Center"
ItemStyle-VerticalAlign="Middle" ItemStyle-Width="250" >
</asp:ImageField>
In my code file
protected void Page_Load(object sender, EventArgs e)
{
DataSourceNew.Selected += new SqlDataSourceStatusEventHandler(DataSourceNew_Selected);
}
protected void DataSourceNew_Selected(object sender, SqlDataSourceStatusEventArgs e)
{
if (e.AffectedRows == 0)
{
dvNew.ChangeMode(DetailsViewMode.Insert);
}
}