You : Excuse me. Do you mind taking us pictures?
Stranger : Sure?
You : Thank you. You can just press the button here.
You : Excuse me. Can you take pictures for us please?
Stranger : Certainly. Is everything set?
You : Please move to the left a bit. Thank you.
You : Excuse me. Can you do me a favor?
Stranger : Sure.
You : We'd like to ask you to take a picture for us.
Stranger : ok.... All right, ready, one... two....
You : Thanks a lot
You : Excuse me. Do you have time to take a picture for us?
Stranger : Oh. I am sorry. I really have to go.
You : It's ok.