<3
Maybe you can. These two certainly seem to be demonstrating it!
He takes the photo and studies it and it's less family resemblence and more the obvious period it was taken and the background knowledge he has (he can't remember if it was Spike who told him directly about having killed his mother, or Ianto indirectly, but he's gleaned it from somewhere) that makes it obvious who this must be.
He lifts a sympathetic gaze to Spike's face. "Your mother?"