There are three steps you need to follow:
- have an "Author" page, which links to your Google+ profile with rel="me"
- have a link to your "Author" page on your post, which contains rel="author"
- have a link from your Google+ profile to your "Author" page (in "Contributor to" section)
Here are the full instructions on how to technically implement this. It should take you about 10 minutes, and I've waited for about a week for Google's search results to actually start displaying my profile picture.
This feature has been available for quite some time, but I still see many bloggers that haven't implemented it yet, also because its availability was mostly unnoticed. Combining search and social is definitely an advantage Google (still) has over Facebook, and they should've made more promotion about this interesting upgrade. Bloggers are content creators, and you want as many content creators inside your social network as possible. They are the ones who provide original thoughts that others are looking for and will eventually follow.
It's hard to estimate if this fact (and different pictures) will have any significant impact on search traffic, I'll keep you posted. But before everyone has it, it's a nice little feature that makes your results look different and much more appealing. Good job, Google, content is king, and you should stay its steward.