Don't know anything about Visual Basic language. But maybe it would help.
1 2 3 4 5 6 7 8 9 10
PictureBox1.visible = False
PictureBox2.visible = False
PictureBox3.visible = False
If a = 0 Then
	PictureBox1.visible = True
ElseIf a = 1 Then
	PictureBox2.visible = True
ElseIf a = 2 Then
	PictureBox3.visible = True
End If