Auto-resizing for images/max width for images?

Hi! First of all I hope this is the right section for this question, I wasn't sure.

So, I've just started using Atahualpa for my Wordpress blog and so far I'm loving it. There's something I'm wondering though. I'd like to be able to have some feature/setting enabled that'll keep content, specifically images, in posts from stretching the layout and jutting out into my righthand menu. So I was wondering if there's some way to either make images auto-adjust their size to the window they're in, or to implement a max width for images on my blog as a whole? Are either of these doable? Or is my best option here simply to not upload images that are too big?

Thanks in advance!
SilverLining