download bmml source – Wireframes created with Balsamiq Mockups
Personally I prefer the text below, but that's a personal preference and there's no real right or wrong answer. It depends on a lot of things, including your content, what you prefer, what the image is of, etc.
Try it both ways on your specific project and see which one works for you. As long as it's close enough to the image to be associated with it in the users' mind, then you'll be in the clear. I know lots of sites actually use a border or background around both the caption and image so that they're clearly seen associated with each other.
download bmml source
Again, there's no right or wrong answer here. It's up to your preference, and you should try both to see which looks best to you and best suits your content. Just make sure to keep pictures and captions close together so they're associated together (I keep re-iterating that, but it's because it's important).