Search Image file in Server Folder (Directory) in ASP.Net

Here I have created sample that will help you out.

HTML

<div>
    <table style="width: 50%; border: none">
        <tr>
            <td>
                Enter Certifice No:
            </td>
            <td>
                <asp:TextBox ID="txtCertificeNo" runat="server"></asp:TextBox>
            </td>
            <td>
                <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
            </td>
        </tr>
    </table>
    <div>
        <asp:Image ID="ImageCertificate" runat="server" Visible="false" />
    </div>
</div>

C#

protected void Button1_Click(object sender, EventArgs e)
{
    ImageCertificate.ImageUrl = string.Format("Certificate/{0}", txtCertificeNo.Text);
    ImageCertificate.Visible = true;
}

Screenshot