Originally Posted by HellCell

Yeah, it's tricky. There's a pixel limitation like 250 x 170 for an extended avatar. Re-sizing could compress or stretch out an image to where it looks warped or pixelated.

A custom image of course you'd have more options with, but that doesn't seem to be what you're looking for.
As for real pictures without being specifically designated to a certain resolution, it stumps me as I don't have an answer to that on top of my head. I'm sure there are ways around it. But I'm going to have to think about it and do some research.

Originally Posted by J.R.R. Tolkien

There is only one bright spot and that is the growing habit of disgruntled men of dynamiting factories and power-stations; I hope that, encouraged now as ‘patriotism’, may remain a habit! But it won’t do any good, if it is not universal.