private void Form1_Load(object sender, EventArgs e)
        {
 
              Bitmap img1= new Bitmap ("D:\\Documents and Settings\\Sonia\\Desktop\\sonia1.bmp");
              Bitmap img2 = new Bitmap("D:\\Documents and Settings\\Sonia\\Desktop\\sonia2.bmp");
              bool a;
           a= doImagesMatch(img1,img2 );
        }
 
 
            public bool doImagesMatch( Bitmap bmp1,  Bitmap bmp2)
            {
            try
                {
 
                 //each image to a byte array
                 ImageConverter converter = new ImageConverter();
                 //create 2 byte arrays, one for each image
                 byte[] imgBytes1 = new byte[1];
                 byte[] imgBytes2 = new byte[1];
 
              //convert images to byte array
              imgBytes1 = (byte[])converter.ConvertTo(bmp1, imgBytes2.GetType());
              imgBytes2 = (byte[])converter.ConvertTo(bmp2, imgBytes1.GetType());
 
            //now compute a hash for each image from the byte arrays
            SHA256Managed sha = new SHA256Managed();
            byte[] imgHash1 = sha.ComputeHash(imgBytes1);
            byte[] imgHash2 = sha.ComputeHash(imgBytes2);
 
 
            //now let's compare the hashes
 
            for (int i = 0; i < imgHash1.Length && i < imgHash2.Length; i++)
             {
                if (!(imgHash1[i] == imgHash2[i]))
                return false;
 
        }
    }
 
            catch (Exception ex)
               {
              MessageBox.Show(ex.Message);
             return false;
               }
                    return true;
                } 
    }

 Public Function doImagesMatch(ByVal bmp1 As Bitmap, ByVal bmp2 As Bitmap) As Boolean
        Dim converter As ImageConverter = New ImageConverter()
        Dim i As Integer
        Dim imgBytes1 As Byte() = New Byte(1)
        Dim imgBytes2 As Byte() = New Byte(1)
    imgBytes1 = (byte())converter.ConvertTo(bmp1, imgBytes2.GetType());
 
        imgBytes2 = (byte())converter.ConvertTo(bmp2, imgBytes1.GetType());
        Dim sha As SHA256Managed = New SHA256Managed()
 
        Dim imgHash1 As Byte() = sha.ComputeHash(imgBytes1)
 
        Dim imgHash2 As Byte() = sha.ComputeHash(imgBytes2)
        For i = 0 To imgHash1.Length And imgHash2.Length
            If ((imgHash1(i) <> imgHash2(i))) Then
                doImagesMatch = False
            Else
                doImagesMatch = True
            End If
        Next
 
    End Function

Dim img1 As Bitmap =  New Bitmap("D:\\Documents and Settings\\Sonia\\Desktop\\sonia1.bmp") 
              Dim img2 As Bitmap =  New Bitmap("D:\\Documents and Settings\\Sonia\\Desktop\\sonia2.bmp") 
              Dim a As Boolean
           a= doImagesMatch(img1,img2)
    End Sub
 
 
            Public Function doImagesMatch(ByVal bmp1 As Bitmap, ByVal bmp2 As Bitmap) As Boolean
            Try
 
                 'each image to a byte array
                 Dim converter As ImageConverter =  New ImageConverter() 
                 'create 2 byte arrays, one for each image
                 Dim imgBytes1() As Byte =  New Byte(1) {} 
                 Dim imgBytes2() As Byte =  New Byte(1) {} 
 
              'convert images to byte array
              imgBytes1 = CType(converter.ConvertTo(bmp1, imgBytes2.GetType()), Byte())
              imgBytes2 = CType(converter.ConvertTo(bmp2, imgBytes1.GetType()), Byte())
 
            'now compute a hash for each image from the byte arrays
            Dim sha As SHA256Managed =  New SHA256Managed() 
            Dim imgHash1() As Byte =  sha.ComputeHash(imgBytes1) 
            Dim imgHash2() As Byte =  sha.ComputeHash(imgBytes2) 
 
 
            'now let's compare the hashes
 
             Dim i As Integer
             For  i = 0 To  imgHash1.Length And i < imgHash2.Length- 1  Step  i + 1
                If Not (imgHash1(i) = imgHash2(i)) Then
                Return False
                End If
 
             Next
            Catch ex As Exception
              MessageBox.Show(ex.Message)
             Return False
            End Try
                    Return True