This phenomenon happens when a pretty girl takes a picture with an ugly girl. Often times the picture is taken as a nice gesture. The next day the pretty girl goes online and finds the picture as the ugly girls profile picture. This effect will make new users who look at the ugly girls profile to think that she is the pretty one. To further this point, the ugly girl may choose to use this picture on a dating site. The passerby will look at the picture and assume that the ugly girl is the pretty girl. Therefore, it is a way of tricking people into thinking that you are pretty without lying.
Tonya: Hey i got a message from a guy on my dating site.
Cait: Wow your so lucky.
Tonya: He wants to see me in the dress i was wearing in the picture
Cait: oh la la
Tonya: Crap, i used the Pity Picture Gone Wrong
Beverly: Hey im checking out everyone's prom pictures online
Hannah: tell me if you find any of me
Beverly: I found one, your with Fat Faced Fiona. AND She is using it as her profile pictures!!
Hannah: no way, now everyone is going to think she is the pretty one in the picture. I hate when a pity picture goes wrong