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Is it illegal to exhibit photographs of people taken in a public place? - photographs of brazillian waxing

For a project I'm working, I photograph people on the street without his knowledge, the photos are then displayed in the window. What are the legal consequences of this situation? I know that there is something more than an invasion of privacy, but people are in a public place, and is Photogrpahers annoying person. Who knows if this is acceptable in the UK? I mean, morally, legally.