title: In Carrierwave how to create a version only when needed? Not when uploading
body: <p>I have setup an uploader to upload a bunch of photos to an album. Then I let the user to select 4 images for the album cover. After they select it, I need to generate a smaller version of the photos. Only the selected 4. How can I do this?</p>
  
  <p>Basically I need a way to generate image versions after the main upload. We can use something like refile. But the problem is, I also need it to create some versions while uploading!</p>