One way of doing it:
For Each PictureBox In Me.Controls
If PictureBox IsNot PictureBox1 AndAlso PictureBox1.Bounds.IntersectsWith(PictureBox.Bounds) Then
collision = True
Exit For 'Exit when at least one collision found
Else : collision = False
End If
Next
This would set collision to False
if PictureBox is indeed PictureBox1. But note that you are overwriting the collision state in each loop, which not what you really want. You should exit the for loop when one collision is found (see my code). You may also change your code like this :
collision = False
For Each PictureBox In Me.Controls
If PictureBox IsNot PictureBox1 AndAlso PictureBox1.Bounds.IntersectsWith(PictureBox.Bounds) Then
collision = True
Exit For
End If
Next