Create config/initializers/paperclip.rb:
```ruby
# http://wiki.github.com/thoughtbot/paperclip/interpolations
Paperclip.interpolates :to_param do |attachment, style|
attachment.instance.to_param
end
```
In the model:
```ruby
has_attached_file :image,
:path => ":rails_root/public/images:to_param/:style/:basename.:extension",
:url => "/images:to_param/:style/:basename.:extension",
:styles => { :large => "250x360#",
:medium => "150x230#",
:small => "110x150#" }
```
Instead of URLs like:
/images/products/249/large/temp.jpg
You can get a URL based on, for example, a permalink as in the example above. In my case I get URLs like this:
/images/games/nintendo-wii/large/super-mario-galaxy.jpg