All you do is render an image. Now you need to extract informatino out of it and processing all pixels to finally receive one(or more) values like "enemy sighted at (x,y)" takes too long. Also low res cameras might not even see the shoe because it's too small.

I know where you're heading but this is really impractical

[EDIT]
You can of course use a neural network to extract features but even this can take a lot of time. Actually a department at my university is working on PCI cards that can implement arbitrary networks with images as input
[/EDIT]