We're generating a photobook with prince and we want to take advantage of the bleed on our printings and put our photos aligned to the outer edge of the page they are on.

right page

| |-------------------------|
| |                         |
| |     /-------------------|
| |     |   image           | image here using text-align: right;
| |     \-------------------|
| |                         |
| |-------------------------|

left page

|-------------------------| |
|                         | |
|-------------------\     | |
|         image     |     | | image here using text-align: left;
|-------------------/     | |
|                         | |
|-------------------------| |

Is it possible to style elements different depending on if they appear on @page:left or @page:right?

You can use "text-align: inside" and "text-align: outside" to align text to the inside or outside of the current two-page spread. There are also margin-inside and margin-outside properties.