i want to make a program written in vb.net which will take text file and a image file,after that the ouput will be the hidden text in a image so that no one can steal data from that image only sender can hide that data in a image and the recipient can unhide that data using key and that application can somebody write a program for hidding data

use encryption techniques like RC4 algo

try this

    'By manipulating the bytes in a picture file this program adds strings to the picture file
    'Without distorting the image
    Public Class Form1
        Dim PicBuffer As System.IO.FileInfo
        Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
            openPic.Title = "Open Picture Files"
        End Sub

        Private Sub openPic_FileOk(ByVal sender As System.Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles openPic.FileOk
            PictureBox1.Image = Image.FromFile(openPic.FileName)
            PicBuffer = New System.IO.FileInfo(openPic.FileName)
            ResizeFileName(openPic.FileName, PicBuffer.Name)
        End Sub

        Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
            Dim Ready As Boolean = True
            Dim PicFileStream As System.IO.FileStream
                PicFileStream = PicBuffer.OpenRead
            Catch ex As Exception
                Ready = False
                MsgBox("Please load a picture before clicking this button", MsgBoxStyle.Critical, "Error")
            End Try
            If Ready = True Then
                Dim PicBytes As Long = PicFileStream.Length
                Dim PicExt As String = PicBuffer.Extension
                Dim PicByteArray(PicBytes) As Byte
                PicFileStream.Read(PicByteArray, 0, PicBytes)
                Dim SentinelString() As Byte = {73, 116, 83, 116, 97, 114, 116, 115, 72, 101, 114, 101}
                If RadioButton1.Checked = True Then
                    Dim PlainText As String = TextBox1.Text
                    Dim PlainTextByteArray(PlainText.Length) As Byte
                    For i As Integer = 0 To (PlainText.Length - 1)
                        PlainTextByteArray(i) = CByte(AscW(PlainText.Chars(i)))
                    Dim PicAndText(PicBytes + PlainText.Length + SentinelString.Length) As Byte
                    For t As Long = 0 To (PicBytes - 1)
                        PicAndText(t) = PicByteArray(t)
                    Dim count As Integer = 0
                    For r As Long = PicBytes To (PicBytes + (SentinelString.Length) - 1)
                        PicAndText(r) = SentinelString(count)
                        count += 1
                    count = 0
                    For q As Long = (PicBytes + SentinelString.Length) To (PicBytes + SentinelString.Length + PlainText.Length - 1)
                        PicAndText(q) = PlainTextByteArray(count)
                        count += 1
                    Dim NewFileName As String = buildPic.FileName
                    My.Computer.FileSystem.WriteAllBytes(NewFileName, PicAndText, False)

                ElseIf RadioButton2.Checked Then
                    Dim OutterSearch, InnerSearch, StopSearch As Boolean
                    OutterSearch = True
                    InnerSearch = True
                    StopSearch = False
                    Dim count As Long = 0
                    Dim leftCounter As Long
                    Dim rightCounter As Integer
                    leftCounter = 0
                    rightCounter = 0
                    Do While (count < (PicBytes - SentinelString.Length) And StopSearch = False)
                        If (PicByteArray(count) = SentinelString(0)) Then
                            leftCounter = count + 1
                            rightCounter = 1
                            InnerSearch = True
                            Do While (InnerSearch = True) And (rightCounter < SentinelString.Length) _
                            And (leftCounter < PicByteArray.Length)
                                If (PicByteArray(leftCounter) = SentinelString(rightCounter)) Then
                                    rightCounter += 1
                                    leftCounter += 1
                                    If (rightCounter = (SentinelString.Length - 1)) Then
                                        StopSearch = True
                                    End If
                                    InnerSearch = False
                                    count += 1
                                End If
                            count += 1
                        End If
                    If StopSearch = True Then
                        'leftCounter contains the starting string that is being retrieved
                        Do While (leftCounter < PicBytes)
                            'Bytes need to be converted to an integer 
                            'then to an unicode character which will be the plaintext
                            leftCounter += 1
                        TextBox3.Text = "The Picture does not contain any text"
                    End If

                End If
            End If

        End Sub

        Sub ResizeFileName(ByVal LongFileName As String, ByVal ShortFileName As String)
            If LongFileName.Length > 71 Then
                Dim LongFileNameSize As Integer = LongFileName.Length
                Dim ShortFileNameSize As Integer = ShortFileName.Length
                Dim Cut As Integer = 71 - (5 + ShortFileNameSize)
                Dim i As Integer
                For i = 0 To (Cut) - 1
                For i = 0 To 4
                For i = 0 To (ShortFileNameSize - 1)
                TextBox2.Text = LongFileName
            End If

        End Sub

        Private Sub RadioButton2_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadioButton2.CheckedChanged
            TextBox1.Enabled = False
        End Sub

        Private Sub RadioButton1_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadioButton1.CheckedChanged
            TextBox1.Enabled = True
        End Sub
    End Class

As far as I know there are two approaches to do this (I'm sure that there are more but I only know the following two):
1) Adding you text at the end of the image binary data.
2) Modifying some pixels and write your text in them.

I found the following links that I think will help:
I used leadtools, a third party sdk to do this because it also provided additional image processing features that I needed.

However, if you only want to embed text into your image, I did a quick search and found the following project:

Hum. This really sound as a scam to hide and share virus and spyware. But anyway hope you use the solution as per what you said you are doing. I'm not judging you though.