Image file is not recognized by the 'identify' command. (heroku)
Apparently the new update to Cocaine gem (0.4.0) breaks the file names for Paperclip and ImageMagick. try rolling back to the previous version (0.3.2), it worked for me.
See here:
https://github.com/thoughtbot/paperclip/issues/1038
PS I believe RMagick is no longer needed on Heroku, works fine for me without it