Hi t01714500930,

Check this example. Now please take its reference and correct your code.

HTML

<asp:Image ID="Image1" ImageUrl="~/Tulips.jpg" runat="server" Width="300" Height="300" />
<br />
<asp:Button ID="Button1" runat="server" OnClick="OnDownoad" Text="Download" />

Namespaces

C#

using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

VB.Net

Imports System.Drawing
Imports System.Drawing.Imaging
Imports System.IO

Code

C#

protected void OnDownoad(object sender, EventArgs e)
{
    string watermarkText1 = "© aspsnippet.com";
    string watermarkText2 = "© love";
    string watermarkText3 = "© my";
    string filePath = Server.MapPath(Image1.ImageUrl);
    using (FileStream fs = new FileStream(filePath, FileMode.OpenOrCreate))
    {
        using (Bitmap bmp = new Bitmap(fs, false))
        {
            using (Graphics grp = Graphics.FromImage(bmp))
            {
                Brush brush = new SolidBrush(Color.Red);
                Font font = new Font("Arial", 50, FontStyle.Bold, GraphicsUnit.Pixel);
                SizeF textSize = new SizeF();
                textSize = grp.MeasureString(watermarkText3, font);
                Point position = new Point((bmp.Width - ((int)textSize.Width + 10)), (bmp.Height - ((int)textSize.Height + 10)));
                grp.DrawString(watermarkText3, font, brush, position);

                textSize = grp.MeasureString(watermarkText2, font);
                position = new Point((bmp.Width - ((int)textSize.Width + 10)), (bmp.Height - ((int)textSize.Height + 60)));
                grp.DrawString(watermarkText2, font, brush, position);

                textSize = grp.MeasureString(watermarkText1, font);
                position = new Point((bmp.Width - ((int)textSize.Width + 10)), (bmp.Height - ((int)textSize.Height + 120)));
                grp.DrawString(watermarkText1, font, brush, position);

                byte[] bytes = null;
                using (MemoryStream memoryStream = new MemoryStream())
                {
                    bmp.Save(memoryStream, ImageFormat.Png);
                    string base64String = Convert.ToBase64String(memoryStream.ToArray());
                    string imageUrl = "data:image/png;base64," + base64String;
                    Image1.Attributes.Add("src", imageUrl);
                    bytes = memoryStream.ToArray();
                }

                Response.ContentType = "image/jpeg";
                Response.AppendHeader("Content-Disposition", "attachment; filename=" + Path.GetFileName(filePath));
                Response.BinaryWrite(bytes);
                Response.End();
            }
        }
    }
}

VB.Net

Protected Sub OnDownoad(sender As Object, e As EventArgs)
    Dim watermarkText1 As String = "© aspsnippet.com"
    Dim watermarkText2 As String = "© love"
    Dim watermarkText3 As String = "© my"
    Dim filePath As String = Server.MapPath(Image1.ImageUrl)
    Using fs As FileStream = New FileStream(filePath, FileMode.OpenOrCreate)
        Using bmp As Bitmap = New Bitmap(fs, False)
            Using grp As Graphics = Graphics.FromImage(bmp)
                Dim brush As Brush = New SolidBrush(Color.Red)
                Dim font As Font = New Font("Arial", 50, FontStyle.Bold, GraphicsUnit.Pixel)
                Dim textSize As SizeF = New SizeF()
                textSize = grp.MeasureString(watermarkText3, font)
                Dim position As Point = New Point((bmp.Width - (CInt(textSize.Width) + 10)), (bmp.Height - (CInt(textSize.Height) + 10)))
                grp.DrawString(watermarkText3, font, brush, position)
                textSize = grp.MeasureString(watermarkText2, font)
                position = New Point((bmp.Width - (CInt(textSize.Width) + 10)), (bmp.Height - (CInt(textSize.Height) + 60)))
                grp.DrawString(watermarkText2, font, brush, position)
                textSize = grp.MeasureString(watermarkText1, font)
                position = New Point((bmp.Width - (CInt(textSize.Width) + 10)), (bmp.Height - (CInt(textSize.Height) + 120)))
                grp.DrawString(watermarkText1, font, brush, position)
                Dim bytes As Byte() = Nothing
                Using memoryStream As MemoryStream = New MemoryStream()
                    bmp.Save(memoryStream, ImageFormat.Png)
                    Dim base64String As String = Convert.ToBase64String(memoryStream.ToArray())
                    Dim imageUrl As String = "data:image/png;base64," & base64String
                    Image1.Attributes.Add("src", imageUrl)
                    bytes = memoryStream.ToArray()
                End Using

                Response.ContentType = "image/jpeg"
                Response.AppendHeader("Content-Disposition", "attachment; filename=" & Path.GetFileName(filePath))
                Response.BinaryWrite(bytes)
                Response.End()
            End Using
        End Using
    End Using
End Sub

Screenshot

Downloaded Image