Finding whether a small image is in a big image

[superhero_iceman]

I have the following code, my img1 is big image, and img2 is small image

I think the error is from

If img1.GetPixel(BigX, BigY) <> img2.GetPixel(SmallX, SmallY) Then

    Public 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) = BigX + Math.Ceiling(img2.Size.Width / 2)
                coordinates(1) = BigY + Math.Ceiling(img2.Size.Height / 2)
Exit_of_this_location:
            Next
        Next
        Return coordinates
    End Function

Any advice