<ItemTemplate>
                        <asp:Image ID="image1" runat="server" ImageUrl='<%# GetValue("Approvato") %>'/>
                    </ItemTemplate>

   public string GetValue(string field)
    {

        if((int)Eval(field) > 1)
{
//ritorno un percorso
}

//altrimenti un altro
    }

        <asp:GridView ID="GridView1" runat="server" AllowPaging="True" AllowSorting="True"
            AutoGenerateColumns="False" CellPadding="4" DataKeyNames="id_clinical_profile"
            DataSourceID="SqlDataSource1" ForeColor="#333333" GridLines="None">
            <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
            <Columns>
                <asp:BoundField DataField="study_code" HeaderText="Study code" SortExpression="study_code" />
                <asp:BoundField DataField="therapeutic_area" HeaderText="Therapeutic area" SortExpression="therapeutic_area" />
                <asp:BoundField DataField="condition" HeaderText="Condition" SortExpression="condition" />
                <asp:BoundField DataField="generic_name" HeaderText="Generic name" SortExpression="generic_name" />
                <asp:BoundField DataField="commercial_name" HeaderText="Commercial name" SortExpression="commercial_name" />
                <asp:ImageField HeaderText="Approved" SortExpression="id_status" DataImageUrlFormatString="images/ok.gif"></asp:ImageField>
                <asp:TemplateField>
                    <ItemTemplate>
                         <asp:Image ID="image1" runat="server" ImageUrl='images/ok.gif'/> 
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:HyperLinkField DataNavigateUrlFields="id_clinical_profile" DataNavigateUrlFormatString="profile.aspx?id={0}"
                    Text="Modifica" />
                <asp:HyperLinkField DataNavigateUrlFields="id_clinical_profile" DataNavigateUrlFormatString="index.aspx?id={0}"
                    Text="Elimina" />
            </Columns>
            <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
            <EditRowStyle BackColor="#999999" />
            <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
            <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
            <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
            <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
        </asp:GridView>
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
            SelectCommand="SELECT clinical_profiles.id_clinical_profile, clinical_profiles.study_code, therapeutic_area.therapeutic_area, clinical_profiles.condition, clinical_profiles.generic_name, clinical_profiles.commercial_name, lang.img, status.status FROM clinical_profiles INNER JOIN therapeutic_area ON clinical_profiles.id_therapeutic_area = therapeutic_area.id_therapeutic_area INNER JOIN lang ON clinical_profiles.id_lang = lang.id_lang INNER JOIN status ON clinical_profiles.id_status = status.id_status">
        </asp:SqlDataSource>

public partial class index : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }

    public string GetValue(string field)
    {
        if ((int)Eval(field) > 1)
        {
            return "ok.gif";
        }

        return "ko.gif";
    } 
}