How to handle image file data in a RoR web service/client?

Hi. I'm breaking an existing app out into separate services for
performance reasons, but am not sure about how best to proceed with
handling images.
The model I'm breaking out into a service has multiple images associated
with it. Historically, these were handled with attachment_fu, and moving
forwards (in the service I'm writing), they will be handled with carrier
wave.
The image data will be caught by the client app in a multipart form, as
normal, then the client app's controller will need to pass that image
data on to the web service (along with other attributes) to create the
model in question.
How do people usually handle this? (I've been scouring the web for
hints, but not doing notably well.)
The web service I'm writing uses JSON, but I guess I need to pass binary
data up for image uploads?
Any & all advice, and any pointers to resources that'll teach me, are
gratefully received.
Cheers,
   Doug.