I'm building a mobile photo sharing site in Python similar to TwitPic and have been exploring various queues to handle the image processing.  I've looked into RabbitMQ and ActiveMQ but I'm thinking that there is a better solution for my use case. I'm looking for something a little more lightweight. I'm open to any suggestions.
Are you considering single machine architecture, or a cluster of machines?  Forwarding the image to an available worker process on the same machine or a different machine isn't profoundly different, particularly if you use TCP sockets.  Knowing what workers are available, spawning more if necessary and the resources are available, having a fail-safe mechanism if a worker crashes, etc, gradually make the problem more complicated.
It could be something as simple as using httplib to push the image to a private server running Apache or twisted and a collection of cgi applications.  When you add another server, round robin the request amongst them.
Which queue is most appropriate?