efficient way to compare 2 images?

[madscijr]

A deer must recognize at first glance whether what it sees is harmless or dangerous (such as a wolf)

I don't know, man. Deer are quite retarded. A deer will jump at the slightest twig movement but will watch a 2,000 pound metal machine roar towards it and not budge an inch.

Because the machine doesn't know it and therefore can't classify it (first time): dangerous or not
PS:
There is a video (but where now), about twelve years old, that shows the German Bundeswehr during target practice with howitzers - and about 200 to 300 meters away deer are grazing peacefully. Why? Because they've realized by now that the banging isn't aimed at them.

I love how we can start off talking about comparing images, and before long I'm hearing interesting stories about deer and artillery practice, LoL!