The regime is definitely illegitimate in eyes of the people, as proven by the fact that most people stayed away from the sham election where their only choices was between archconservatives and reactionaries.
the context of international relations,
The US has had no diplomatic relations with Iran since 1979 and does not recognize that regime as legitimate.
and control.
Yes they do control people. With torture and murder. But torture and murder is not really viewed as a legitimate way for countries to control their population.