Not illegal, but be gracious and get permission
Websites like mrtcrush.com that encourage people to take and submit photos of strangers are not doing anything wrong, said Mr Rajan Supramaniam, a lawyer at Hilborne Law LLC
He said: "Taking photos in public places is generally all right. As long as they are not for commercial use and if there are no derogatory or defamatory remarks."
He said there was a grey area when you post the pictures online, especially if they are accompanied by personal or sexual remarks.
If a complaint is lodged, the parties involved can be investigated.
Mr Supramaniam said: "It borders on infringing on people's privacy although it's in a public place.
"For ethical reasons, you should get permission from the people in the photos if you want to post them."
Mr William Wan, general secretary of the Singapore Kindness Movement, agreed saying: "To be gracious, it is necessary to ask permission before you post it. Kindness includes respect for the privacy of (other) people.
"It is only courteous and if you intend it to be positive (to compliment someone), there is no reason why you should not ask for permission."
While appreciating the website creators for promoting "cyber-complimenting", Mr Wan said: "It is encouraging that we have people who are tired of the negativity and want to do something positive, but we must be sensitive to the privacy needs of people and be aware of unexpected consequences.
"Good intentions do not always lead to good consequences."