We had the need to dynamically generate new images after an attachment is uploaded. For example, our designer might need a non-standard image size to fit a new template, or a client would be customizing their site and need a smaller version of their uploaded image.
To accomplish this, I created a gem that overrides the Paperclip::Attachment.method_missing to take resize parameters. The gem is called attachment_on_the_fly, and it's located at http://gemcutter.org/gems/attachment_on_the_fly.
In order to use this gem, install it, require it in a model using Paperclip, and call it using methods like this:
I chose not to use a Processor because Processors only fire when the save method is called, and this did not work with my team's workflow.
If you find this functionality useful, feel free to integrate it with Paperclip (I can make a patch for you), send me comments, ideas, issues, etc.
I think what would be better would be letting you maintain the gem, while we make a link to your project. Thanks a lot for making this! :D