Another image aligning problem

I can’t get the image to stay in the center of the post, regardless of size. It always ends up shifting to the right, doesn’t matter if I choose “center” or not in the post/write/text box. The ONLY way for it to stay in the center is to make the image the exact pixel which is 470 wide. But it’s not possible to make ALL my images that size; sometimes I’ll have to post a picture smaller than 470 wide. If it’s smaller than that, it’ll shift to the right, and when you click into the permalink, the picture will pop out vertically of the text box altogether. Hmph.

Well regardless of pixel size, is there a code I can place in either those php or css files to fix this?

Thanks!

PS. Check my blog, the latest post:
http://www.niquehappy.com/blog/

Click into the first post, you’ll see what I mean.