ASP.NET

<asp:TemplateField ItemStyle-Width="22px">
  <ItemTemplate>
    <asp:ImageButton ID="imbView" runat="server" ImageUrl="~/Images/ViewSearch.gif"  />
  </ItemTemplate>
</asp:TemplateField>         
<asp:TemplateField ItemStyle-Width="22px">
  <ItemTemplate>
    <asp:ImageButton ID="imgEdit" runat="server" ImageUrl="~/Images/Edit.gif"  />
  </ItemTemplate>
</asp:TemplateField> 
<asp:TemplateField ItemStyle-Width="22px">
  <ItemTemplate>
    <asp:ImageButton ID="imgDelete" runat="server" ImageUrl="~/Images/Delete.gif"  />
  </ItemTemplate>
</asp:TemplateField>                       
<asp:TemplateField ItemStyle-Width="22px">
  <ItemTemplate>
    <asp:ImageButton ID="imgPrint" runat="server" ImageUrl="~/Images/Print.gif"  />
  </ItemTemplate>
</asp:TemplateField>

</asp:HyperLinkField DataNavigateUrlFormatString="~/Invoices/Invoice.aspx?id={0}&Readonly" DataNavigateUrlFields="InvoiceID" ItemStyle-Width="20px" />
</asp:HyperLinkField DataNavigateUrlFormatString="~/Invoices/Invoice.aspx?id={0}&Edit" DataNavigateUrlFields="InvoiceID" />
</asp:HyperLinkField DataNavigateUrlFormatString="~/Reports/Reports.aspx?DeleteFromSomeWhere" DataNavigateUrlFields="InvoiceID" />
</asp:HyperLinkField DataNavigateUrlFormatString="~/Reports/Reports.aspx?id={0}" DataNavigateUrlFields="InvoiceID" />

public void dgData_onRowDataBound(Object src, GridViewRowEventArgs e)
{
  if (e.Row.RowType == DataControlRowType.DataRow)
  {
    DataRowView row = (DataRowView)e.Row.DataItem;
    HyperLink link = (HyperLink)e.Row.Cells[0].Controls[0];
    if (!(link == null))
    {
      link.ImageUrl = "~/Images/ViewSearch.gif";
      link.ToolTip = "Print";
    }
    link = (HyperLink)e.Row.Cells[1].Controls[0];
    if (!(link == null))
    {
      link.ImageUrl = "~/Images/Edit.gif";
      link.ToolTip = "Print";
    }
    link = (HyperLink)e.Row.Cells[2].Controls[0];
    if (!(link == null))
    {
      link.ImageUrl = "~/Images/Delete.gif";
      link.ToolTip = "Delete Invoice";
      link.Attributes.Add("onclick", "javascript: alert('works'); return false;");
    }
    link = (HyperLink)e.Row.Cells[3].Controls[0];
    if (!(link == null))
    {
      link.ImageUrl = "~/Images/Print.gif";
      link.ToolTip = "Print Invoice";
    }
  }
}

        if (!(link==null))
        {
          link.ImageUrl = "~/Images/ViewSearch.gif";
          link.ToolTip="Print";
          link.Width = System.Web.UI.WebControls.Unit.Pixel(20);
          e.Row.Cells[0].Style.Add("max-width", "20px");
          e.Row.Cells[0].Style.Add(System.Web.UI.HtmlTextWriterStyle.Width, "20px");
          e.Row.Cells[0].Width = System.Web.UI.WebControls.Unit.Pixel(20);
        }
and also
  <asp:HyperLinkField ... ItemStyle-Width="20px" ControlStyle-Width="20px"/>