I had no clue that I have freedom photograph almost anything I want in public. As I recall, even my friends did not. May be you don’t know this, have a read. This is written keeping US in mind, but now I am almost sure this must be applicable in most of the countries. Off to Google it …

Public Spaces

Under current US legislation, you are entitled to photograph anything that you want to from a public space and that includes people and things, except where a specific law prohibits such activity.

Private Property
Photography on private property is subject to the permission of the property owner. Note the use of the word ‘on’. Owners of private property have no right to prohibit photography from a public space, even if the subject of the photography is their private property. If a property owner asks you to stop taking photographs while you are on their property, you are legally obliged to obey. If you wish to take photographs on private property, ask permission, state your reasons and usage and you may be allowed. It’s amazing how a polite request can bring its own reward.

Exclusions
These are pretty obvious. Military installations can be, and most are, restricted, so don’t even bother. Nuclear energy facilities are restricted although the publicly visible areas may not be restricted but generally speaking, consider the whole area as restricted as it varies from installation to installation and is not worth the hassle of confrontation.

People are fair game while in a public place except in areas where they would reasonably expect privacy, such as in their own homes, toilets, dressing rooms and medical installations.

Popular Misconceptions
The following is a list of subject matter that invariably leads to a confrontation. There is NO LEGAL RESTRICTION to photographing any of the following from a public space.

Accidents and fire scenes
Children (this one, while legal, may cause great offence, so use common sense)
Celebrities
Bridges and other infrastructure
Residential and commercial buildings
Industrial facilities and public utilities
Transportation facilities (e.g., airports)
Superfund sites
Criminal activities
Law enforcement officers

and further if you are interested.