When using facial recognition to unlock your device, your phone can indeed be unlocked by someone or something that looks like your image. As facial recognition is less secure than all the other options available, we do recommend using one of those for security. Additionally if you use your face as a screen lock method, your face cannot be used to unlock the screen when turning on the device. To use the device, you must unlock the screen using a pattern, PIN, or password you set when registering the face.
We will certainly pass on your desire for the iris scanner to our Development Team.