AJAX Photo Uploading the Easy Way with Rails 4 and Paperclip - JustPayme

In creating JustPayme (Week 5 of the 20/20 Challenge), the most important step was the simple on-boarding of a new user and their card.  On reaching the site, the user travels through a three step form, as displayed in the gallery below:

The step that often trips me up is what to do with photo uploading.  In this case, I wanted the user to be able to choose a file, preview it, and then submit it when they are ready.  In addition, this whole form would have to be submitted through AJAX so that we could continue the user flow and move on to the final step of the on-boarding process.