Several possibilities here:
Path
You're using a relative path
You say it's in a view - view paths are based on the assets/images
folder. So it can't be relative, as it already is. I would recommend removing the relative path, and basing it on the assets/images
folder structure, like this:
<%= image_tag('slider/new_york_2.jpg') %>
Precompile
If you're using Heroku, you have to precompile your assets
This keeps consistency & is quite simple to do:
#config/production.rb
config.serve_static_assets = true
Then when you deploy to Heroku, you should do this:
rake assets:precompile RAILS_ENV=production
This should help!