Researchers use a mirror test to determine whether subjects perceive mirrors reflections as belonging to them. While dogs have failed this test, this doesn't necessarily mean they lack self-awareness -- only that the mirror doesn't engage their interest.
When dogs look into a mirror, they typically have one of two responses: They may bark or try to invite play as if they were staring at another dog, or they may appear to do nothing. Dogs who perceive the mirror reflection as another dog and either bark or invite the dog to play tend to lose interest when their actions get no response. After this first experience, they often ignore their reflection in the mirror.
This behavior suggests that dogs don't understand they are looking at themselves in the mirror. Dogs fail to pass the so-called mirror test, a test that determines whether a species perceives the mirror reflection as its own. Species that have passed this test include dolphins, chimpanzees, orangutans, gorillas and elephants.
The Mirror Test
To test whether an animal perceives the reflection as its own, researchers paint a few red dots on the animal's face and watch the animal's reaction. Animals who pass the mirror test see the red dots on their face in the mirror and start to touch their own face. This demonstrates that they see they dots as being on their face. Animals who fail the mirror test, including dogs, do not display interest in their mirrored reflection when they red dots are on their face.
Just because your dog won't pass the mirror test does not mean your dog has no self-awareness. University of Colorado biologist Marc Bekoff attributes this to dogs' behavior and preference for scent-based information over visual information. While dogs can and do see the world, smell is their prime way of experiencing information. He performed a "yellow snow" test to see if a dog could recognize his own urine over that of other dogs, and his dog passed.