Image source: Philip Morris.Like its former tobacco-giant parent, Philip Morris International (NYSE: PM) has rewarded its shareholders with substantial dividend growth. In less than a decade, Philip Morris has boosted its dividend eight times, and investors expect that a ninth increase is likely to come within the next month. Yet looking beyond that, Philip Morris is now facing some challenges it hasn't had to deal with before, and some dividend investors fear that its payout growth could remain much slower than it was in past years.