We have a 1 1/2 yr. old German Shepherd who can act like she doesn't know who we are. She has been like this since we got her at about 3 mos. old. I've never had a dog act like this before. Today it was a bit unnerving because I was walking back from getting the mail and the dog crouched down and looked like she could attack. Even after I spoke to her she acted strange. She finally recognized me. I worry that things could get worse with her. Any one have any ideas? Safety comes first.
Without having more information, my advice to you, if safety is your main concern (which is should be) is bring the animal to an animal care expert and trainer.
Some trainers can ID ingrained behavioural problems and possible causes. Remember: animals can also experience mental illness, which can cause erratic behaviour.
Your dog may have vision/hearing/olfactory issues which interfere with identifying you, which an animal care expert may also be able to identify.
My mother brought a dog with very odd behaviour to a trusted animal care expert who referred her (the dog) to a vet for proper diagnosis of epilepsy which it turned out the dog had. In other cases you could be looking at various neurological disorders, some of which can lead to dangerous behaviours.
But this is all speculation. Your dog could be fine and this may just be idiosyncratic behaviour. Get the dog looked at.