So far, I have found this. I put it in application.rb
# Needed for paperclip: http://github.com/thoughtbot/paperclip/issues/issue/247
# The documentation states that custom processors that inherit
from Paperclip::Processor will be loaded
# automatically if placed in lib/paperclip_processors. But in
Rails 3, this isn't the case.
# This issue is caused by the Paperclip gem being loaded before
the Rails object is properly configured.
# Needs to be fixed properly in Paperclip itself.
# copied from paperclip.rb: due to bundler, this doesn't seem to
happen automagically anymore!?!
"paperclip_processors", "*.rb")).each do |processor|
require processor # PVDB don't rescue LoadError... let it rip!