If that is the statutory definition of "pornography" in your state, then having a minor pose smoking a cigarette is not "pornography," despite the fact that it is intended to be erotic, because it is not "sexually explicit." Indeed, the whole basis of SF --or any fetish for that matter, is sublimation, i.e. sexual arousal in response to acts or objects which are not in themselves sexually explicit.

There could be laws on the books in other states which define pornography in more general terms, which might then be the basis for criminal charges. But due process requires that criminal statutes be very specific as to what is being prohibited, and the state must prove each and every element of the offense as defined.

But that's all just legalism. Legality and morality do not always coincide, and this is a good example. Vesperae gives as good a test for the morality of it as any, i.e. if you would be comfortable actually having sex with the SF model, then you should be comfortable watching a video of her smoking.

Personally, I do not like to see obviously young models smoking and I find it a real turnoff. I know that some sites have offered such images and I avoid all such material. Some are more ambiguous, however, and it is easy to get fooled --whether or not there is an age disclaimer for the models. At least one site has offered mums and daughters smoking together, which suggests that the activity is being endorsed by a parent. Still, I avoid these videos even though I might find the mum to be a very attractive smsoker. Ultimately, the best you can do is just apply your own personal comfort test, as V suggested.