that depends on what kind of photo you want to take.
If it's candid shots, of course you can't approach them and ask them politely! normally candid shots are the among the most beautiful of all pictures, i feel. Just lift your camera, and FIRE FIRE FIRE. then quickly pretend to look up and gaze OVER the subject. If he/she asks, just say, oh behind you got some really nice things.
If you want to do a posed portraiture, it helps if you can give some ID. like oh I'm from a magazine, or you can pretend to do some interview (your skin's so clear, what do you use, etc. etc.)
One thing about Singapore is that people here are very camera-shy. If you go overseas, they'll more than gladly pose for you, especially if they know you are a tourist. So tough luck, just keep on trying and you'll be rewarded though. I always believe in that.
If it's a digital cam like the Coolpixes, or the G2 with the swivel out LCD, just look down at the LCD and aim, at them pretend to poke a few buttons. That way if they notice you they might think you are just fiddling around. They might suspect, but the doubts will hold them back long enough for you to take a few shots.
i would be pointing my cam @ something else near them....then juz shoot and leave...if they noticed me...then i'd juz smile @ them...most of the time they don't notice cos i dun think they'd be thick-skinned enuff to say that I'm taking their pictures...heee~
Reminds me.... On saturady... Me was fiddling with my cam when this guy thought I was shooting him... Came over and ask me. When I say No and smile he left. But he keep looking at me as I'm finishing my cigarette...
Not easy to hide my gigantic D5... Usually I shoot and then run, or smile at them then take pic (During events) or shoot from hip. Having larger (pixels wise) pic allows you to crop more when shooting from hip. occasionally I'll use my 250mm and take picture of them from afar. Another way is to pretend to shoot something above them then look down and pretend to preview the image as you shoot them. And putting a flash unit that is bigger than your camera can give impression that you are some guy on a job, helps. Hee Hee
Me still don dare to ask for permission to take photos...usually me stand far away and try to zoom in as much as possible...
Even when taking children pic in bugis fountain, where lotsa ppl take photos of kids playing the water, I still stand at a distance and take...
Think me need to train to be a little more thick skin
Do U think Singapore gals will pose if I go to them and ask?