In a method of manufacturing an image sensor, photodiodes may be formed on a semiconductor layer in an active pixel region and a peripheral region. A structure including insulating interlayers and wiring structures may be formed on a first surface of the semiconductor layer in the active pixel region, the peripheral region and an input/output (I/O) region. The semiconductor layer and a first insulating interlayer of the insulating interlayers on the I/O region may be partially etched to form a via hole exposing a first wiring structure of the wiring structures. A first metal layer and a second metal layer may be formed on a second surface of the semiconductor layer and the via hole. The second metal layer may be patterned to form a second pad pattern on the semiconductor layer in the I/O region. An anti-reflective layer may be formed on the first metal layer and the second pad pattern. The anti-reflective layer and the first metal layer may be patterned to form a light blocking structure including the first metal layer and the anti-reflective layer in the peripheral region, and a pad structure including a via contact, a first pad pattern, the second pad pattern and an anti-reflective pattern in the I/O region. An image failure due to the reflected light may be minimized.