I think there's a resemblance in the ears, nose and hairline. It was not as apparent to me when the only comparison photographs I had seen were ones with each directly facing the camera. But my first (and lasting) impression from previous pictures was that they don't appear to be related.
The photos posted by Fred Nerks at #81 above show a far stronger resemblance between OBH and Malcolm because of the similarities of their gummy smiles and teeth. Regardless, he's the spawn of someone with an evil agenda for America.
I looked at those too, and don't see the resemblance in those features.
Obama Senior's nose is much shorter than Junior's, from tip to bridge. Junior has defined ear lobes, while Senior doesn't. The hair lines don't match at all, from what I can see. Foreheads don't match, cranial shapes are different, facial constructions don't match, etc.
Hard as I try, I just can't see any resemblance between these two. My guess is, Stanley Ann chose Senior as a designated paternal unit for some unknown reason. She either didn't know who the real father was, or intentionally concealed his identity because it would have been unsafe to reveal it.