Centering images

Hi,

I'm trying to center images on my website: http://cargocollective.com/soundofthought

i put this code at the top of my CSS feed;
.project_content img { float: none !important; }

and then put this wrapped around the specific image that i want to center;

<center>{image 1}</center>

however as you can see, it's not exactly in the center.

I'm pretty new to this whole coding thing, so if you could step by step explain this to me that would be appreciated.

cheers,
bryce