Photography requires -almost- no technical skills anymore. Modern cameras are able to perfectly expose a scene most of the time.

That alone doesn't make good images, though.

What is it, then? What's the difference between greatness and mediocrity in photography?

Talent -as in a naturally given ability to appreciate beauty- plays a role in this.

A lack of talent can be overcome, though, by anyone who possesses what I believe is the key to great art: passion.

While technical skills and talent can give a photographer a head start, only passion will bring them beyond the point where photographers without it can't go.