Question: I wish to inquire about a ruling regarding kissing the feet of elders [and] prostration out of respecting a human being (sujud al-ta`dhim).... If the kissing or touching was practised in the posture of prostration, [is this] unlawful (haram) and one of the major sins?
Prostration to other than Allah with the intention of worship is disbelief; with the intention of respect, prohibited (haram).
Kissing a parent's or teacher's foot with the intention of respect is neither even if it seems to resemble it outwardly.
These are separate issues and should not be confused.
The hadiths in which the Companions kissed the foot orfeet of the Prophet, upon him blessings and peace, are known. Imam Muslim asked for permission to kiss the foot of Imam al-Bukhari. It is difficult to imagine anyone kissing another's foot other than in a posture seeming to resemble prostration to some, and it would be an outlandish suggestion that imitating the Companions of the Prophet (Allah bless him and give him peace) and the great early Muslims could be among the major sins.
So if it is permissible - and it is permissible – then it is permissible unconditionally, not only if it does not resemble prostration.
It is the same with those that forbid bowing to someone and therefore kissing the hand because it involves bowing (because it is impermissible to bow to another). It is poor reasoning.
As Imam Habib Mashhur al-Haddad said in Key to the Garden as translated by Sidi Mostafa Badawi: Friend, you will bow to pass through the low door of this mosque then again to pick up your children or kiss them - and there is nothing wrong with it. Or something to that effect.
As for difference of sex then the same ruling that applies to touch applies here regardless of kissing or prostrating.
There remains two remarks:
1. If a certain culture over-emphasizes a gesture of adab and tends to make it an obligation, new rulings may apply. If the obligation is a social custom with no religious connotation it is a mere innovation.
Examples are the expectation of an elderly Turkish woman that a greeting male kiss her hand, even a non-mahram, or the expectation among certain Gulf Arabs that a proper greeting between males involves kissing cheeks/lips and rubbing noses.
If the obligation acquires a religious connotation it is an innovation of misguidance which must be avoided.
2. Whether contemporary people kiss hands and feet out of unthinking imitation or have anything like the Companions' high sense of dignity on the one hand and their pure, forthright, selfless, and trusting hearts on the other, is another matter.
I ask forgiveness if I said anything wrong and beg to be corrected by those Allah will reward.
And Allah knows best
Answered by Shaykh Gibril Haddad of the Hanafi fiqh list.