I have watched some pornographic video that shocked me. In many videos a nude girl walks in very crowded public places in the blatant view of other people. I thought that it might be a video trick, but I think it is real.
Is this really legal in some countries? If so ...
In which countries is it legal to be nude in public and what pragmatic value is it providing for that society?
Yes, public nudity is legal in many countries, but it varies by community dependent upon what is considered indecent exposure. In Scandinavia, Barcelona, the United Kingdom, and Canada for example it is legal to be naked in public in some circumstances like sunbathing, skinny dipping, or similar activities.
What constitutes indecent exposure depends on the standards of decency of the community where the exposure takes place. These standards can vary from the very strict standards of modesty in places such as Afghanistan and Saudi Arabia, which require most of the body to be covered, to tribal societies such as the Pirahã or Mursi where full nakedness is the norm.
As for what practical purpose public nudity serves, that would be the lack of harm public nudity causes others and therefore it is a matter of personal liberty.
In the UK the test is reasonable assumption of intention. So if one were naked but there was no reason to assume that your intention was to offend then no law has been broken. A lot of the time though the police will move you on so if you are taking artistic nude landscape images you had better be ready to be (a) extremely polite and (b) state your understanding of the law, your (and your models) intention(s) to make art not offense and your shared willingness to leave just as soon as you are done.
Other countries differ considerably due to custom, social mores and other cultural elements.
Nothing is illegal until a law is made to forbid it.
Some societies haven't found real reasons to forbid nudity and it is still common in some tribes in Amazon and other places around the world.
Your question is biased, the actual question should be: what is the pragmatic value of forbidding nudity?
If there is any, then some societies may not have found it yet, or law enforcement may be unnecessary because nudity is not common anyway.
Countries like the Scandinavian countries, and to a lesser extent, the UK, Canada and "progressive" parts of Spain (Barcelona is very far left, perhaps like Berkeley, California) take a relaxed attitude toward sex generally. Since they aren't "uptight" about the one thing, they aren't uptight about the other thing that is often associated with the former.
Arab and other countries that have strict laws against nudity are those that basically frown upon pre-marital "activities." They legislate against the one as a means of discouraging the other.
What the law is in any given place is based on what the overall ethos is (strict or permissive), and that's why public nudity is more tolerated in some places than others.
As for Russia, it is illegal, but at worst you will be fined by an equivalent of 50 dollars or so.
A video made by a random witness in Kazakhstan:
http://www.youtube.com/watch?feature=player_embedded&v=C7VkpXfuDB4
I am quite sure that in some other countries (namely Canada) it is completely legal.
