HyperLinkFieldImageUrl.aspx font size:
C# source: HyperLinkFieldImageUrl.aspx   plan_details.aspx   
<%@ Import Namespace="System.Data" %>

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

<script language="C#" runat="server">
   public void getImages ( Object src, GridViewRowEventArgs e ) {
      if ( e.Row.RowType == DataControlRowType.DataRow ) {
         DataRowView rowView = ( DataRowView ) e.Row.DataItem;
         string planId = rowView [ "PlanId" ].ToString ( );

         TableCellCollection myCells = e.Row.Cells;
         HyperLink planLink = ( HyperLink ) myCells [ myCells.Count - 1 ].Controls [ 0 ];
         planLink.ImageUrl = string.Format ( "~/shared/images/plans/thumbs/{0}.jpg", planId );
         planLink.ToolTip = rowView [ "Model" ].ToString ( );
      }
   }
</script>
</head>

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

<div align="center">
<form runat="server">
   <asp:gridview id="myGrid" runat="server"
      datasourceid="plans"
      width=98% cellpadding=5 font-size="9pt"
      gridlines="horizontal"
      showheader=false
      autogeneratecolumns=false
      allowpaging pagesize=5
      onRowDataBound="getImages">

      <rowstyle backcolor="ghostwhite" verticalalign="top" />

      <pagersettings
         position="topandbottom"
         mode="numericfirstlast"
         nextpagetext="Next" previouspagetext="Prev" />

      <pagerstyle
         backcolor="darkslategray"
         forecolor="khaki"
         font-bold
         horizontalalign="right" />

      <columns>

         <asp:boundfield
            datafield="Design" />
         <asp:boundfield
            datafield="Model" 
            itemstyle-forecolor="navy"
            itemstyle-font-size="10pt"
            itemstyle-font-bold />
         <asp:boundfield
            datafield="Description" />
         <asp:boundfield
            datafield="PlanID"
            itemstyle-horizontalalign="right" />

         <asp:hyperlinkfield
            datanavigateurlfields="planid"
            datanavigateurlformatstring="plan_details.aspx?id={0}">
            <controlstyle borderwidth=1 borderstyle="inset" />
         </asp:hyperlinkfield>

      </columns>

   </asp:gridview>

   <asp:accessdatasource id="plans" runat="server"
      datafile="~/app_data/plans.mdb"
      selectcommand="SELECT Design, Model, Description, PlanId FROM Plans 
         WHERE Type in ( 'English', 'French', 'Tudor', 'Victorian' )" />

</form>
</div>

<!-- #include virtual="~/shared/viewsrc.inc" -->

</body>
</html>