Save Default Image to database if no image selected in FileUpload in ASP.Net

First you need to add a default image and name it as Default.png and place it in your project.

And the using the reference of the following article I have created this.

HTML

<asp:FileUpload ID="FileUpload1" runat="server" />
<asp:Button ID="btnUpload" runat="server" Text="Upload" OnClick="Upload" />
<br />
<asp:Label ID="lblMessage" runat="server" Text="" Font-Names="Arial"></asp:Label>
<hr />
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField DataField="Id" HeaderText="Id" />
        <asp:BoundField DataField="Name" HeaderText="Name" />
        <asp:TemplateField HeaderText="Image">
            <ItemTemplate>
                <asp:Image ID="Image1" runat="server" ImageUrl='<%# ToBase64(Eval("Data")) %>' />
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Namespaces

using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.IO;

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.GridView1.DataSource = GetData("SELECT Id, Name, Data FROM tblFiles");
        this.GridView1.DataBind();
    }
}

protected string ToBase64(object data)
{
    byte[] bytes = (byte[])data;
    string base64String = Convert.ToBase64String(bytes, 0, bytes.Length);
    return "data:image/png;base64," + base64String;
}

private DataTable GetData(string query)
{
    DataTable dt = new DataTable();
    string constr = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(query))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.CommandType = CommandType.Text;
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                sda.Fill(dt);
            }
        }
        return dt;
    }
}

protected void Upload(object sender, EventArgs e)
{
    string filePath = string.Empty;
    string contenttype = string.Empty;
    string filename = string.Empty;
    byte[] bytes = null;
    if (this.FileUpload1.HasFile)
    {
        filePath = FileUpload1.PostedFile.FileName;
        filename = Path.GetFileName(filePath);
        string ext = Path.GetExtension(filename);
        contenttype = string.Empty;

        switch (ext)
        {
            case ".jpg":
                contenttype = "image/jpg";
                break;
            case ".png":
                contenttype = "image/png";
                break;
            case ".gif":
                contenttype = "image/gif";
                break;
        }

        using (Stream fs = FileUpload1.PostedFile.InputStream)
        {
            using (BinaryReader br = new BinaryReader(fs))
            {
                bytes = br.ReadBytes((Int32)fs.Length);
            }
        }
    }
    else
    {
        filename = "Default.png";
        contenttype = "image/png";
        System.Drawing.Image defaultImage = System.Drawing.Image.FromFile(Server.MapPath("~/Images/Default.png"));
        using (MemoryStream ms = new MemoryStream())
        {
            defaultImage.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            bytes = ms.ToArray();
        }
    }

    string query = "INSERT INTO tblFiles(Name, ContentType, Data) VALUES (@Name, @ContentType, @Data)";
    string constr = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(query))
        {
            cmd.Parameters.Add("@Name", SqlDbType.VarChar).Value = filename;
            cmd.Parameters.Add("@ContentType", SqlDbType.VarChar).Value = contenttype;
            cmd.Parameters.Add("@Data", SqlDbType.Binary).Value = bytes;
            cmd.CommandType = CommandType.Text;
            cmd.Connection = con;
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();
        }
    }
    lblMessage.ForeColor = Color.Green;
    lblMessage.Text = "File Uploaded Successfully";
    Response.Redirect(Request.Url.AbsoluteUri);
}

SQL

CREATE TABLE [dbo].[tblFiles](
	[Id] [int] IDENTITY(1,1) NOT NULL,
	[Name] [varchar](50) NULL,
	[ContentType] [varchar](100) NULL,
	[Data] [varbinary](max) NULL
) ON [PRIMARY]

GO

Screenshot