VB Timer problem

Here’s a simple bit of VB code, or so I thought!!, that I am having a problem with.

Public Class Form1

    Private Sub Timer1_Timer()
        If image1.Visible = True Then
            image1.Visible = False
            image2.Visible = True
        ElseIf image2.Visible = True Then
            image2.Visible = False
            image1.Visible = True
        End If
    End Sub

End Class

I have added a timer and this appears below the form and have also added two images.

I’m just wondering why the image is staying static and not switching between images 1 & 2

Might it be because I hard coded the below code. Did I need to click on any controls in order to activate this.

Private Sub Timer1_Timer()

End Sub

I would really appreciate any help to get this working.