Is it bad or illegal to picture a car's plate number?

My uncle and i had a very big conflict between us and what is worse is that his car is parked in our condo parking area. I have took a photo of their car but just the front part in order to have a copy of the plate number to show the admin of the building that their car plate number and to know if there can be ways not for him to park here since we are also thinking of our safety against them. The farther we are from each other the better. But the bad part here is that their driver saw me took a photo of their car and report it to my uncle. Now he thinks im going to let him killed. And he is thinking of reporting that if something bad happened to him, i am the one who is responsible for it.

What should i do?
ANd is it illegal to picture a car's plate number?

how is taking a picture related to killing?

nothing illegal.