Add the carrierwave gem.
Use Carrierwave to store a question's image.
Use Carrierwave for an answer's photo.
Add ImageUploader#filename.
Fix the specs for Carrierwave for an answer.
Store the randomly generated portion of a photo's filename in the DB.

https://github.com/jnicklas/carrierwave/wiki/How-to%3A-Create-random-and
-unique-filenames-for-all-versioned-files
Don't send the photo_secure_token from backbone.
Generate a photo's filename based on the secure token.