Carrierwave, creating a duplicate attachment when duplicating its containing model

I don't believe Carrierwave has this option. However, you can make use of the *_remote_url= method to set the new model's picture to be a duplicate of the first.

Here's a brief example

Say I have a model which has_one :photo attached with carrierwave. I can duplicate, the model, set the photo to the previous one and save it. Example:

first_model = User.first
duplicate_model = first_model.dup #(where the dup code duplicates everything else you need)
duplicate_model.remote_photo_url = first_model.photo_url
duplicate_model.save

This would then "copy" the photo from the first object into your second as a new carrierwave attachment.

Try this gem https://github.com/equivalent/copy_carrierwave_file , it handles both local storage and Fog storage

original_resource = User.last
new_resource      = User.new

CopyCarrierwaveFile::CopyFileService.new(original_resource, new_resource, :avatar).set_file    

new_resource.save
nev_resource.avatar.url # https://...image.jpg

While copy_carrierwave_file is a neat gem it is not nescessary as long as you use local storage.
carrierwave can use local files as source of attachments and you can use this to duplicate the attachment:

first_user = User.first
duplicate_user = first_user.dup
duplicate_user.photo = File.open(first_user.photo.file.file) if first_user.photo.present?
duplicate_user.save

This is more efficient than routing the image twice through your web server.