Sanchi, 2nd-1st century CE.
The early twentieth-century writer Alfred Foucher was the first to articulate the theory, which has been universally accepted for nearly a hundred years. He based his ideas on the assumption that the earliest Buddha images were those produced in the Gandhara region of ancient India during the early centuries CE—more than half a millennium after the Buddha was supposed to have lived. In Gandhara, he surmised, artists were influenced by the Greek and classical world, which stimulated the anthropomorphic images of the Buddha.
Nonetheless, a fresh analysis by S. L. Huntington based on archaeological, literary, and epigraphic evidence casts doubt on the practice of deliberate avoidance of Buddha images. Proponents of the theory have contended that the practice of creating anthropomorphic representations of the Buddha was initiated only when Mahayana Buddhism began to flourish around the early centuries CE. However, others have argued that, on the basis of textual evidence, Hinayanists were probably as receptive to the making of images as Mahayanists. Indeed, in the entire corpus of Buddhist literature, scholars have been able to find only a single, indirect reference to a proscription against the creation of Buddha images, and that is limited to the context of a single Buddhist sect.
Huntington argues that most, if not all, of these reliefs do not represent events in the life of the Buddha at all, but rather portray worship and adoration at sacred Buddhist sites. Although some of these reliefs may depict devotions made at sacred sites even while the Buddha was supposedly still alive, most of them probably show the sites as they were worshiped after the lifetime of the Buddha. He also argues that the aniconic symbols, such as empty thrones, trees, wheels, and stupas (topes), were not intended to serve as surrogates for Buddha images, but were the sacred focus of worship at these sites. The reliefs, then, are essentially ‘postcards’ of the sites and show the practices of pilgrimage and devotion associated with them. (Devotees could perhaps have made rubbings of the reliefs and used them for private devotional purposes.)
Relief panel with the Buddha's First Sermon,
Pakistan, ancient region of Gandhara, circa 2nd century CE, Schist 28.6 x 32.4 cm. The Metropolitan Museum of Art.
There could be other explanations: 1) early anthropomorphic images of Buddha may not have survived, or have not been discovered yet. As more ancient images of the Buddha come to light, the aniconic theory will disprove itself; the earliest images of Buddha seem to be on a gold coin (Approx. 130CE) minted by Kushan King Kanishka, and the Bimaran casket (Earliest date 30BCE), and 2) perhaps the early Buddhists didn’t believe in a real Buddha, (there were supposed to have been 25 previous Buddhas in this Aeon alone) and only later, perhaps after the Third Buddhist Council convened by Ashoka circa 250-253 BCE, that a need for a historic founder was agreed upon.Watch the video below (Open Source Buddhist Research Institute - Madison) for a traditional view of Buddhist aniconism.