ButtonFieldImageUrl.aspx font size:
View Sample
<%@ Import Namespace="System.Data" %>

<html>
<head>
<title>Dynamically Generated ButtonField ImageButtons</title>
<link rel="stylesheet" href="/shared/netdemos.css">

<style type="text/css">
.desc {
   font:bold 11pt arial,verdana,sans-serif; background:whitesmoke; 
   border:1px inset; padding:10; margin-bottom:10}
.specs {
   font-size:9pt; background:beige; 
   border:1px inset; padding-right:5}
</style>

<script language="C#" runat="server">
   void Page_Load ( Object src, EventArgs e ) {
      if ( !IsPostBack ) {
         productsList.SelectedIndex = 0;
         productsList.DataBind ( );
         productDetails.DataBind ( );
      }
   }

   public void getImages ( Object src, GridViewRowEventArgs e ) {
      if ( e.Row.RowType == DataControlRowType.DataRow ) {
         DataRowView rowView = ( DataRowView ) e.Row.DataItem;
         string productId = rowView [ "productid" ].ToString ( );

         ImageButton imgButton = ( ImageButton ) e.Row.Cells [ 0 ].Controls [ 0 ];
         imgButton.ImageUrl = string.Format ( "~/shared/images/gear/{0}.jpg", productId );
      }
   }
</script>
</head>

<body>
<!-- #include virtual="~/shared/top.inc" -->
<div class="header"><h2>Dynamically Generated ButtonField ImageButtons</h2></div>
<hr size=1 width=92%>

<form runat="server">
<center>

<table width="96%">
<tr valign="top">
   <td width=50%>
      <asp:gridview id="productsList" runat="server"
         datasourceid="products"
         datakeynames="productid"
         autogeneratecolumns=false
         allowpaging pagesize=5
         cellpadding=5 font-size="9pt"
         gridlines="horizontal"
         onRowDataBound="getImages">

         <headerstyle backcolor="steelblue"
            forecolor="beige" />

         <rowstyle verticalalign="top" />

         <columns>

            <asp:buttonfield
               buttontype="image"
               commandname="select">
               <controlstyle width=75
                  borderwidth=1 borderstyle="inset" />
            </asp:buttonfield>

            <asp:templatefield>
               <itemtemplate>
                  <table>
                  <tr>
                     <td>Item:</td>
                     <td><asp:linkbutton runat="server"
                        text='<%# Eval ( "ProductName" ) %>'
                        commandname="select" style="color:navy" /></td></tr>
                  <tr>
                     <td>Price:</td>
                     <td><%# Eval ( "Price", "{0:c}" ) %></td></tr>
                  </table>
               </itemtemplate>
            </asp:templatefield>

         </columns>

         <selectedrowstyle backcolor="palegoldenrod" />

      </asp:gridview>
   </td>

   <td>
      <asp:formview id="productDetails" runat="server"
         datasourceid="details"
         enableviewstate=false>

         <itemtemplate>
            <img runat="server" 
               src='<%# Eval ( "ProductID", "~/shared/images/gear/{0}.jpg" ) %>' 
               alt='<%# Eval ( "Model" ) %>'
               width=220 height=220 border=0>
            <br>
            <div class="desc">
               <%# Eval ( "Description" ) %>
            </div>
            <div class="specs">
               <%# Eval ( "Specs" ) %>
            </div>
         </itemtemplate>

      </asp:formview>
   </td></tr>
</table>

<asp:accessdatasource id="products" runat="server"
   datafile="~/app_data/gear.mdb"
   selectcommand="SELECT ProductId, Brand + ' ' + Model AS ProductName, Price FROM Products 
      WHERE Type='Stove'" />

<asp:accessdatasource id="details" runat="server"
   datafile="~/app_data/gear.mdb"
   selectcommand="SELECT * FROM Products"
   filterexpression="ProductId='{0}'">

   <filterparameters>
      <asp:controlparameter controlid="productsList" propertyname="SelectedValue" />
   </filterparameters>

</asp:accessdatasource>

</center>
</form>

<hr size=1 width=92%>
<!-- #include virtual="~/shared/viewsrc.inc" -->

</body>
</html>