Is there a way to align two elements?

Specifically, I'd like to align an image and it's caption.

(While I'm asking: how do I tell the caption to autonumber the image, eg Fig 2.3, and then reference it elsewhere?)

Thank you.

There are text-align and vertical-align properties, it really depends what kind of alignment you are trying to achieve. Automatic numbering can be done using counters and cross-references.

Thank you.

I'd like to align the left edges of the image and its caption, and put the caption a fixed distance below the image.

If you were using this HTML markup for images and captions:

<div class="image"><img src="myimage.jpg"/></div>
<div class="caption">This is a caption!</div>

Then they would be left aligned by default, and you could add vertical spacing between them by adding bottom margin to the image and/or top margin to the caption.