Your attachment contains binaries - could you remove them and reattach the zip.
But the following should work for you.
Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
Dim p As PictureBox
For Each c As Control In Me.Controls
If TypeOf c Is PictureBox Then
p = DirectCast(c, PictureBox)
p.Visible = False
End If
Next
End Sub