I have the following code, I want to do pixel by pixel comparison between the big and small image

My questions are
1. How I can write to the coordinate? coordinates{0, 0} = BigX + Math.Ceiling(img2.Size.Width / 2) does not seem right
2. How I can change the size of the coordinate from one point to XX points? XX will be input to the function as a new ByVal



Code:
    Private Function ImageCompare(ByVal img1 As Bitmap, ByVal img2 As Bitmap)
        Dim coordinates(,) As Integer = {{-1, -1}}
        For BigX = 1 To img1.Size.Width - img2.Size.Width + 1
            For BigY = 1 To img1.Size.Height - img2.Size.Height + 1
                For SmallX = 1 To img2.Size.Width
                    For SmallY = 1 To img2.Size.Height
                        If img1.GetPixel(BigX, BigY) <> img2.GetPixel(SmallX, SmallY) Then
                            GoTo Exit_of_this_location
                        End If
                    Next
                Next
                coordinates{0, 0} = BigX + Math.Ceiling(img2.Size.Width / 2)
                coordinates[{0},{1}] = BigY + Math.Ceiling(img2.Size.Height / 2)
Exit_of_this_location:
            Next
        Next
        Return coordinates
    End Function