Este sera el codigo .aspx
<body>
    <form id="form1" runat="server">
    <div>
    
        <asp:FileUpload ID="FileUpload1" runat="server" />
        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" 
            Text="Vista Previa" />
        <br />
        <asp:Button ID="Button2" runat="server" Text="Nombre de Archivo" />
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:Image ID="Image1" runat="server" />
    </div>
    </form>
</body>Y este codigo sera del lado del servidorCode Behind :
string imgname;
    protected void Page_Load(object sender, EventArgs e)
    {
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string L_path = "No Images";
        imgname = FileUpload1.FileName;
        TextBox1.Text = imgname;
        // break the pathe, collect file type then match.
        string filetype;
        filetype = System.IO.Path.GetExtension(FileUpload1.PostedFile.FileName);
        if (filetype.ToLower().Contains(".jpg")  ||  filetype.ToLower().Contains(".jpeg") || filetype.ToLower().Contains(".bmp") || filetype.ToLower().Contains(".png"))
        {
            ClientScript.RegisterStartupScript(typeof(string), "You choosen the file in wrong formated.. !!!", "");
        }
        if (FileUpload1.PostedFile.ContentLength > 5242880) // byte size
        {
            Page.ClientScript.RegisterStartupScript(Type.GetType("System.String"), "addScript", "alert('Image Size is should be Less Than 5 MB' )", true);
        }
        if (FileUpload1.HasFile)
        {
            L_path = Server.MapPath("~/Images/").ToString();
            L_path += imgname;
            FileUpload1.SaveAs(L_path); // Temporary saved 
        }
        else
        {
            Page.ClientScript.RegisterStartupScript(Type.GetType("System.String"), "addScript", "alert('No Image is Selected..)", true);
        }
        Image1.ImageUrl = "~/Images/" + imgname;
        Page.ClientScript.RegisterStartupScript(Type.GetType("System.String"), "addScript", "alert('Image is Reflected..Plz Save it)", true);
        // After saving into Database delete current file from Application.
    }


Y Después para guardarla en una Base de Datos Sql o en una carpeta en la misma aplicación
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