A T-Rex's vision is based on movement. Although, I'm not sure if that was ever really proved.
There's a degree of truth to this - ever see a rabbit freeze up? Either when you get near it, or it'll run for a little while then suddenly stop? Vision based predators, like hawks, can lose track of prey if they suddenly stop moving. However, it's not that they CAN'T see them, it's just they're tracking an expected path which suddenly stops. If they just saw a rabbit sitting there, they could figure it out.
I'm going to call shenanigans on any predator as complex as a T-Rex being unable recognize something that isn't moving as prey. If that was true, they'd be p**s poor carrion eaters, and any animal that big is going to HAVE to eat some carrion...