Then really you need to check with them about their ticket terms and conditions. Most events will/should have conditions to the effect of "by purchasing this ticket and attending the event you agree to have your image used to publicise the event" etc.
Whether you're charging or not is irrelevant, but the difficult one will be your first scenario - ticketed customers wandering public areas - as it'll be difficult to judge who's a customer and who's not unless you remember them!