I'm not sure exactly how it works, but this is amazingly accurate. Read the  full description before looking at the picture.

The picture below  has 2 almost identical dolphins in it.  It was used in a case  study on stress level at St. Mary's Hospital.  Look at both  dolphins jumping out of the water. The dolphins are   identical.   A closely
monitored, scientific study of a group  revealed that in spite of the fact that the dolphins are identical, a  person under stress would find differences in the two dolphins. If there  are many differences found
between both dolphins, it means that the person  is experiencing a great amount of stress.
Look at the photograph  and if you find more than one or two differences you may want to take a  vacation.