Is it legal to take photos of someone as evidence?

Hi again,

Is it legal to take photos of someone  – NOT CHILDREN – as evidence that the person is damaging  common property?

We have a problem with an owner feeding birds and would not stop as well as denying that he feed the birds so we start taking photos of him feeding birds on balcony.

Our managing agent send him the final warning to stop. He denied the accusation and have ask for evidence and we did show him the photos.

Now our managing agent send us a letter saying. 

It has been bought to our attention  that a members of the executive committee have been taking surveillance photographs of the another occupier

at the building.

This is illegal, an invasion of privacy and is to cease immediately.

Every time we have a problem in this building people always say where is your evidence? notes is not enough for them as they always said we need visual not note. So where do we stand in this as owners protecting their property?