I also believe Logan is the MiB. The hat color is the clue and the MiB is bald to hide his true identity. Perhaps William is the one who helps the androids become free, hence the white hat.

at one point I thought perhaps Ford was responsible for his brother and fathers' death, having killed his brother, then father upon discovery and ended up becoming a serial killer. The android family is his sick homage. It might explain why Teddy appears to be human at some point in time, then became an android.

But, none of this accounts for Arnold. I'm lost.

I think the clue in the photo is that Bernard cannot see himself inn it. He is standing to the left of the android in the void space we see to the right in the photo.