A small imager mounted on a user's eye (referred to as a femtoimager) is coordinated with an external camera. The femtoimager may be contained in a contact lens, and it may be aligned with the gaze a user's eye. The femtoimager and external camera capture images with overlapping views of the external environment. Images from the two imagers may be compared with one another to estimate the femtoimager's view of the external environment relative to the camera's view of the external environment. This may then be used for different applications.