Is the worshipper behind the imam required to say the opening Takbir (Takbirat al-Ihram) himself?

The opening takbeer (Takbeerat al-Ihram) is a pillar of prayer, and the prayer is not valid without it for both the Imam and the follower, due to the Prophet's (peace and blessings of Allah be upon him) saying: "The key to prayer is purification, its consecration is the takbeer, and its desacralization is the tasleem." As for the other takbeers, they are a Sunnah and not obligatory, but the follower should not intentionally abandon them, due to the Prophet's (peace and blessings of Allah be upon him) saying: "And when he says 'Allahu Akbar', then say 'Allahu Akbar'."