Image caption alignment

I've got custom CSS to make my image captions align left without the em dash, but I'd really like them aligned with the left hand edge of the actual image (so a space of about 1 character before the text). Is this possible please? Also, the left alignment doesn't seem to work when the image is in a thumbnail grid - it's centred under the image. Ideally I'd like text to be centered across the grid but I can't see how to do that. Next best thing would be left aligned under the first image. http://www.vintagevagabonds.net/?p=1237