title: Rails PaperClip Attachments, knowing if there's a image thumbnail?
body: <p>I'm using Rails 3 paperclip and allow users to upload attachments to the attachment model.</p>
  
  <p>If the file is an image, the app generates image previews. If the file is not, it only uploads the file (no image previews).</p>
  
  <p>Now I would like to display a list of all the attachments in the DB. So I use attachment.attachment(:large) and that works fine for image attachments, but errors (obviously) for non-image attachments.</p>
  
  <p>What's a good way to check if it's an image attachment or not? If not, I'd like to display a standard static image. Any suggestions? thanks</p>