Activity
I like #4 personally :)
What does it look like when the image does not load? Does it show up as a 404?
This is one of my favorites. https://pchm.co/posts/tutorial-how-to-build-a-cms-in-ruby-on-rails
In that case Gem or Engine is probably your best option. Check out this tutorial for some ideas on how engines could be used :) https://pchm.co/posts/tutorial-how-to-build-a-cms-in-ruby-on-rails
Depending on what you're doing it may be worth extract the code into a Gem or an Engine.
Git Submodules is also a viable option. I've started using them to share common CSS and JS code between different rails apps.