Currently there is no support for image rotation in Asciidoctor. There is support for rotating font-based icons, so if you have them enabled, you could use the Font Awesome styles to perform rotation. Something like:
image::images/fig_12_nyc.jpg[role=fa-rotate-90]
Of course, you could put these in your custom stylesheet and then use any role you want. CSS has the ability to rotate elements.
We could consider promoting these styles to the default stylesheet (and we may have already proposed such an idea).
-Dan