I am not a lawyer (that's the second time today), but I believe that while the US may influence (threaten/bribe/etc) other countries to follow these procedures, your rights as a passenger are still determined by the individual country in question. (By analogy for example, if a US citizen is arrested overseas, they don't necessarily have the same rights that they would have if they were arrested in the US.)

In the US, the TSA are "required" to post signs about the nude-o-scope, "required" to allow you to opt out, required to have the perve in the backroom, etc. Other countries could, if they chose, have no warning about the nude-o-scope*, not allow people to opt out**, or have a 100" monitor on the wall showing your nude-o-scope image to all the other passengers waiting in line***.

* Of course, it appears many US airports conveniently forget to have the signs, too.
** I'm looking at you, United Kingdom of Great Britain and Northern Ireland.
*** While this would be humiliating for the first two or three people through the line, it would increase the opt-out rate substantially!