What I know, is that the third eye is located on your forehead between your brows. Pictures draw the eye horizontally or vertically but always in the same location. Hinduism, Buddhism, and many other natural practices believe in the 7 energy wheels along the vertebra known as the 7 Chakras, one of them (The 6th Chakra) is called The Third Eye Chakra.
This energy point is connected to clairvoyance and intuition or “seeing the bigger picture” in terms of spirituality, being conscious of the physical body and the other dimensions that you may not see with your naked eye. For me, this is the most legit meaning, explaining the phenomenon of the “Third Eye”.
On another note, the eye can be seen as the symbol of intelligence or some may say “illumination”. Someone with higher knowing and divine purpose connected to the universe and all its secrets.