Where is the line drawn with stealing? It's obvious what stealing is when engaged-in often. You take the stuff of others while under a certain mental state, that mental state being marked and noticeable by an understanding that something isn't under your possession (but under another's), and physical effort to appropriate it regardless of the other person's wishes.

So if someone is happy with you 'stealing' something, is that stealing? In general, no, as this would be a gift.

On the other hand, we have situations such as copyright law, or other ideas where the line of 'possession' is inappropriately drawn.

So here is the problem. What is the meter by which we can say something is stolen or not? It can't be the sweeping idea, 'this is my property', as that idea can be faked, as in the case of intellectual property. It can be a case where there is appropriate and inappropriate mental possession of items, and stealing only being the violation of the appropriate lines.

Is it fully intent? Kamma = Intent, so if you do not engage in the intent of stealing, you will not experience the results. However, what if you are someone who considers smelling the flowers of another individual stealing? Surely that would not be considered stealing, yet to that person smelling the flowers would trigger the intent. Even though that coarse mental intent would arise, as far as I know that is not actual stealing, so the 'non-intent stealing' would not have an object. At which point can you say you are actually stealing, and at which you are not?

It is really simple with coarse events but hard with complex contexts. Taking an apple from someone without asking is stealing, but what about abusing sales at a market? - what about when those sales are glitches, unintended, in the system? - what about liberally charging a corporate card?

For our modern, daily situations a really subtle understanding of the precepts is required. So where is the subtle line of stealing?
‘If a monk, intending to steal, takes from a village or from the
  wilderness what has not been given to him— the sort of theft for which
  kings, having caught a thief, would beat, imprison, or banish him,
  saying, “You’re a bandit, you’re a fool, you’ve gone astray, you’re a
  thief”— he too is expelled and not in communion.’ Second Parajika rule 


This is for monks, but it's pretty clear - or at least it leaves the subjectivity to individual jurisdictions! (so in Italy, if you are starving and steal food, it's ok. If it's less than the value of a good shield (1/4 dinar), then in Sharia countries you are not in trouble)

With regards to possession, who possesses and to what extent, are probably useful measures. Who possesses is usually well defined (if not, then theft becomes a gray area). To what extent - how long should patents and copyright last, whether you can even effectively charge for something like streetlighting - are all likely subject to a social consensus. 

Overall, if you perceive the object of your desire to be in the possession of someone else, or that someone else directly tells you so (asking is always a nice way to establish possession), then any intentional act to take such a thing, against the wishes of the owner would be theft, regardless of social consensus. 

Piracy and claims as to the injustice of any and all economic systems are ancient claims, modernity only offers a novel spin on them.

If you think/believe/know that within a jurisdiction, a thing is claimed by someone and they don't have any desire to relinquish it, intentional taking of it is theft. Whether that possession is rightfully in their hands or not, is for their kamma, not yours.