The first thing that impresses is definitely its name!
The so-called «Thatcher effect» is nothing more than an impressive optical illusion that was given the name of the “iron Lady” just because its creators used it for the first time in the photo of British Prime Minister.
The second thing that surprises is that nothing seems strange in the inverted picture, aside from the fact that the depicted face is … upside down! Once the photo returns at the right place, the mystery is solved and the effect is revealed! But how is this possible?
It is very difficult for the viewer to identify local changes in the characteristics of an inverted face (eyes, nose, eyelids, etc.), although these changes are evident in the “normal” face. Therefore, the Thatcher effect is the following:
Image in the normal position has overturned eyes, nose, mouth or eyelids, which can be clearly seen. However, once the same image is turned over, the alterations in the characteristics disappear as if by magic, i.e. the viewer sees a normal image turned upside down! It is believed that this phenomenon occurs due to some psychological processes involved in face recognition and coordinated in the normal upright faces.