เช็คชื่อรูปไม่ให้ซ้ำกับข้อมูลใน database จะเขียน code อย่างไรดีครับ

<table class="auto-style1" id="tb">
            <tr>
                <td class="auto-style2">ศิลป วัฒนธรรม</td>
                <td>
                    <asp:DropDownList runat="server" ID="ddlIDart" DataSourceID="sqlIDart" DataTextField="name_art" DataValueField="id_art"></asp:DropDownList>
                    <asp:SqlDataSource runat="server" ID="sqlIDart" ConnectionString='<%$ ConnectionStrings:backendConnectionString %>' SelectCommand="SELECT [id_art], [name_art] FROM [art_culture]"></asp:SqlDataSource>
                </td>
            </tr>
            <tr>
                <td class="auto-style2">รูปภาพ</td>
                <td>
                    <asp:FileUpload ID="FileUpload1" runat="server" />
                </td>
            </tr>
            <tr>
                <td class="auto-style2">&nbsp;</td>
                <td>
                    <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="บันทึก" Width="103px" />
                    <asp:Label runat="server" ID="lblsave" ForeColor="Green"></asp:Label>
                </td>
            </tr>
        </table>

        protected void Button1_Click(object sender, EventArgs e)
        {
            {
                if (FileUpload1.HasFile)
                {

                    string str = FileUpload1.FileName;

                    FileUpload1.PostedFile.SaveAs(Server.MapPath(".") + "//image_art//" + str);

                    string path = "~//image_art//" + str.ToString();

                    DataTable dt;
                    String SQL = "insert into [art_image] ([name_image_art], [id_art]) values ('" + path + "', '" + ddlIDart.SelectedValue + "')";
                    var connstring = ConfigurationManager.ConnectionStrings["backendConnectionString"].ConnectionString;
                    using (SqlConnection conn = new SqlConnection(connstring))
                    {
                        using (SqlCommand comm = new SqlCommand(SQL,conn))
                        {
                            conn.Open();
                            using (SqlDataAdapter da = new SqlDataAdapter(comm))
                            {
                                dt = new DataTable("tb");
                                da.Fill(dt);
                                
                            }
                            conn.Close();
                            lblsave.Text = "บันทึกเรียบร้อย";
                            Response.Redirect("insert_image_art.aspx");
                        }
                    }
                }

            }
        }