It would be incorrect to assert that there were not a series of Councils held by Bishops which condemned Iconoclasm prior to the Seventh Ecumenical Council of 787 (i.e. the Second Council of Nicea). In fact, almost as soon as the heresy arose, condemnations of the heresy, not just by individuals, but by Synods transpired. Let us give a few examples below.
In the 720s, Emperor Leo III the Isaurian published edicts ordering the removal and destruction of iconography, in league with heretical bishops; this was opposed by Patriarch St. Germanus. However, Patriarch St. Germanus was expelled by the heretics, and in his place the Pseudo-Patriarch Anastasius, a supporter of iconoclasm, was put in his place. This called forth massive resistance, breaking of communion, and the eventual anathematization of iconoclasm in a formalized setting at the 731 Synod of Rome. The 8th Century Liber Pontificalis contains the following entries relevant to this, first beginning with Pope St. Gregory II.
