How the data is embedded in the image

Question

please explain this code clearly !!! how the file is embedded inside the image and retrieved back !!!
 Private Sub btn4(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NLabel4.Click
        Using O As New OpenFileDialog With {.Filter = "(Image Files)|*.jpg;*.png;*.bmp;*.gif;*.ico|Jpg, | *.jpg|Png, | *.png|Bmp, | *.bmp|Gif, | *.gif|Ico | *.ico", .Multiselect = False, .Title = "Select image"}
            If O.ShowDialog = 1 Then
                Try
                    Using FS As New IO.FileStream(O.FileName, IO.FileMode.Open)
                        FS.Seek(0, IO.SeekOrigin.End)
                        While Not FS.ReadByte = Asc("|")
                            FS.Position -= 2
                        End While
                        Dim s As String = Nothing
                        While Not FS.Position = FS.Length - 4
                            s &= Chr(FS.ReadByte.ToString)
                        End While
                        Dim Ext As String = Nothing
                        FS.Seek(0, IO.SeekOrigin.End)
                        While Not FS.ReadByte = Asc("*")
                            FS.Position -= 2
                        End While
                        While Not FS.Position = FS.Length
                            Ext &= Chr(FS.ReadByte.ToString)
                        End While
                        FS.Seek(FS.Length - ((s.Length + s) + 5), IO.SeekOrigin.Begin)
                        Using sfd As New SaveFileDialog With {.DefaultExt = Ext, .Filter = "*." & Ext & " | *." & Ext}
                            If sfd.ShowDialog = 1 Then
                                Using FSw As New IO.FileStream(sfd.FileName, IO.FileMode.Create)
                                    While Not FS.Position = FS.Length - (s.Length + 5)
                                        FSw.WriteByte(FS.ReadByte)
                                    End While
                                End Using
                            End If
                        End Using
                    End Using
                Catch ex As Exception
                    MessageBox.Show("There was an error!" & vbNewLine & vbNewLine & "The application will now close.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                    Me.Close()
                End Try
            End If
        End Using
    End Sub
    Private Sub btn3(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NLabel3.Click
        Dim ext As String = TextBox1.Text.Substring(TextBox1.Text.LastIndexOf(".") + 1)
        Using SFD As New SaveFileDialog With {.DefaultExt = ext, .Filter = "*." & ext & " | *." & ext}
            If SFD.ShowDialog = 1 Then
                Try
                    Dim ImageBytes() As Byte = IO.File.ReadAllBytes(TextBox1.Text)
                    Dim FileBytes() As Byte = IO.File.ReadAllBytes(TextBox2.Text)
                    Dim FS As New IO.FileStream(SFD.FileName, IO.FileMode.CreateNew)
                    FS.Write(ImageBytes, 0, ImageBytes.Length)
                    FS.Write(FileBytes, 0, FileBytes.Length)
                    FS.WriteByte(Asc("|"))
                    Dim FileSize() As Byte = System.Text.ASCIIEncoding.ASCII.GetBytes(New IO.FileInfo(TextBox2.Text).Length)
                    FS.Write(FileSize, 0, FileSize.Length)
                    FS.WriteByte(Asc("*"))
                    Dim Extention() As Byte = System.Text.ASCIIEncoding.ASCII.GetBytes(TextBox2.Text.Substring(TextBox2.Text.LastIndexOf(".") + 1))
                    FS.Write(Extention, 0, Extention.Length)
                    FS.Close()
                    FS.Dispose()
                    MsgBox("Done")
                Catch ex As Exception
                    MessageBox.Show("There was an error!" & vbNewLine & vbNewLine & "The application will now close.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                    Me.Close()
                End Try
            End If
        End Using
    End Sub

Answer 1

1. the new file which we are creating will be in this order or not 
file_extension * data_file_size | data_file image_file
No.  The file will be in the order in which it is written in the writing routine:
1. Image File
2. Data File
3. "|"
4. Data File Size (ASCII)
5. "*"
6. File Extension (ASCII)
2. explain this snippet .. why we are changing position while we are extract file
 While Not FS.ReadByte = Asc("|")
                            FS.Position -= 2
                        End While
                        Dim s As String = Nothing
                        While Not FS.Position = FS.Length - 4
                            s &= Chr(FS.ReadByte.ToString)
                        End While
                        Dim Ext As String = Nothing
                        FS.Seek(0, IO.SeekOrigin.End)
                        While Not FS.ReadByte = Asc("*")
                            FS.Position -= 2
                        End While
                        While Not FS.Position = FS.Length
                            Ext &= Chr(FS.ReadByte.ToString)
                        End While
                        FS.Seek(FS.Length - ((s.Length + s) + 5), IO.SeekOrigin.Begin)
The file read position is recalculated before each read, depending either on the position of the marker ("|" and "*") or on the length of the data.   That's how each portion is extracted - the position is set to the start of the portion, and that
portion is read for the correct number of bytes.  The portions are extracted from the end back towards the beginning because the markers can only be guaranteed as unique (they are illegal in a filename extension) when searching backwards.
3. after combining the files with the image .. how the created image is visible (even we are not using any algorithm)
That depends on the image file format, but most formats will use header information that describes the location within the file of the various bits of data that are needed to create the image.  The side effect of this is that if there is information
in the file that is not referenced from this header data then it is simply ignored.  That's what this procedure is relying on - because the new data is appended to the end of the file it will not be referenced from the header data and will be ignored.
For a complete description of what this code does and why it works you should refer to the original author.