What is the ruling on a worshipper differing with his imam in some of the postures of prayer, such as those found in the book "The Prophet's Prayer Described" by Sheikh Al-Albani, and the imam prohibiting the worshipper from not following him?

There is no harm in praying behind any Imam whose prayer is valid (complete in its conditions and pillars, and free from invalidating factors), even if the Imam follows a different madhhab (school of thought) from the follower. If agreement in madhhab were a condition, people would scatter, and congregational prayer would become impossible. Sheikh al-Islam Ibn Taymiyyah issued a fatwa permitting followers of some madhhabs to pray behind followers of others, even if they differed on issues that some consider to invalidate prayer. He stated that the prayer of one who prays behind an Imam who differs from him in madhhab is valid, even if the Imam performs an act that would invalidate the prayer according to the follower's madhhab.