High load image processing architecture for web

I have to implement the following high-load application:

Users send images to a web-server via browsers. Server should process images and send results (several strings) to user's browsers back. Results should appear in 10 seconds and Html-UI should be resposive (non blocked) while server processing.

What do you think about the following architecture, are technologies are appropriate and solution is scalable?

1. There are several web-servers (~2-4) that are ready to get user images.
2. When the image is received it's deligated to one of processing-servers (there should be ~50 processing servers in local network that are not accessible from Internet)
3. (a) Client starts to poll web-server if processing result is ready via ajax with interval (1000 ms.)
4. (b) Client has flash/silverlight c开发者_Python百科omponent that implements duplex browser <-> web-server channel to receive results from server as soon as results are ready.

There are some vapour things in that:

1. Would you personally prefer ajax polling approach or duplex communication (with flash/silverlight) in Internet environment? Or will you mix them ?
2. How web-server should know that processing results are ready? I guess there should be single fast-responsive mediator service in local internet that is notified by processing servers (up to 50 processing servers) with processing results and notifies web-servers that results are ready.

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What you need is a framework for parallel processing. Take a look at:

http://gearman.org/