In other countries, they have very strict laws regarding privacy. So much so that in some cases, you'll notice that cars do not have licence plates on the front bumper, because traffic/speed cameras may only photograph a car from behind, to protect the identity of the driver. Imagine, even their gahmen mata cannot take their photo! So it is very well possible for someone to sue your pants off for taking his picture, especially if it so happens to be on private property.
Here in Sg, is different. Like someone already mentioned, taking pics of ppl is not against the law (provided you don't defame the person). This is why sites like sggirls.com can still continue to operate. The last I checked, lah.