The device itself is likely tamper resistant, has built in DRM and will have a high fidelity camera + signal processor. So you will need a system to write a 200MP image on the surface the size of an eye ball.

Also, since the light passes through a lens in your eye, there are probably optical tricks that can validate the surface is curved like a retina and has been distorted by a lens.

Oh yeah. And the vascularization of the retina means that you can view heart rate pulses. So your image will need to pulsate too.

One could also imagine marrying this with a stereoscopic camera to image detect that a real face is. It could even ask you to smile or frown to validate it's a real face.

Lots of ways to harden this technology to the point where even intelligence agencies would struggle to defeat it.