Single Image Caption Overflow

I am trying to have a single image show on a post along with its caption. I had great success using info from this posting:http://ww.wp.xz.cn/support/topic/plugin-next-gen-gallery-singlepic-caption.

What I need now is for the caption to be the same width as the image (which can vary). This was also a problem mentioned in the solution.

Any thoughts would be really helpful.

http://ww.wp.xz.cn/extend/plugins/nextgen-gallery/