I do mine the same way that you do. Sometimes I draw with pencil, charcoal or use a brush with a thin oil wash.
I use photos because most of my work is of animals, dogs, cats, cows donkeys etc. and animals just won’t sit still long enough to paint them from life. :)
But I never project the photo and trace it, I do not own a protector.
I don’t care who does, I just don’t like to see students do it and make big bucks selling their paintings to unsuspecting people.
***I use photos because most of my work is of animals***
Most of us use them to a certain extent. It was Muybridge’s photos of the horse in action that changed illustrations forever from rocking horse style horses to real action horses.