Topic: Production assets and picture upload questions

Hello I have a few questions that came up while trying to learn proper production techniques.

I have a production server I am working on right now which is an Ubuntu 12.04 with nginx as a load balancer and static content server and it uses a unicorn unix socket for the dynamic content

Sometimes it complains about uncompiled assets after I run rake assets:precompile. The image it complains about is a url to an image hosted on another server am I not supposed to use image_tag for that or am I missing something else?

I am planning on creating functionality for user uploaded images. I was wondering what good practices there are to allow this in production. If I make a folder in public called images and organize and upload them there will rails complain about uncompiled assets or does that only apply to public/assets.

Thanks everyone,
Hope all is well