Hi  sampp18,
I have created sample that full fill your requirement.
HTML
<div>
    <table>
        <tr>
            <td>
                <asp:TextBox ID="txtImage" runat="server"></asp:TextBox>
            </td>
            <td>
                <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
            </td>
        </tr>
    </table>
    <div>
        <asp:Image ID="img" runat="server" Visible="false" />
    </div>
</div>
Code
VB
Protected Sub Button1_Click(sender As Object, e As EventArgs)
	img.ImageUrl = String.Format("Images/{0}.jpg", txtImage.Text.Trim())
	img.Visible = True
End Sub
C#
protected void Button1_Click(object sender, EventArgs e)
{
    img.ImageUrl = string.Format("Images/{0}.jpg", txtImage.Text.Trim());
    img.Visible = true;
}
Screenshot
