favicon installation for Ruby on Rails apps (application.html.erb)

favicons

    <!-- For third-generation iPad with high-resolution Retina display: -->
    <!-- Size should be 144 x 144 pixels -->
    <%= favicon_link_tag 'apple-touch-icon-144x144-precomposed.png', :rel => 'apple-touch-icon-precomposed', :type => 'image/png', :sizes => '144x144' %>

    <!-- For iPhone with high-resolution Retina display: -->
    <!-- Size should be 114 x 114 pixels -->
    <%= favicon_link_tag 'apple-touch-icon-114x114-precomposed.png', :rel => 'apple-touch-icon-precomposed', :type => 'image/png', :sizes => '114x114' %>

    <!-- For first- and second-generation iPad: -->
    <!-- Size should be 72 x 72 pixels -->
    <%= favicon_link_tag 'apple-touch-icon-72x72-precomposed.png', :rel => 'apple-touch-icon-precomposed', :type => 'image/png', :sizes => '72x72' %>

    <!-- For non-Retina iPhone, iPod Touch, and Android 2.1+ devices: -->
    <!-- Size should be 57 x 57 pixels -->
    <%= favicon_link_tag 'apple-touch-icon-precomposed.png', :rel => 'apple-touch-icon-precomposed', :type => 'image/png' %>

    <!-- For all other devices -->
    <!-- Size should be 32 x 32 pixels -->
    <%= favicon_link_tag 'favicon.ico', :rel => 'shortcut icon' %>

Old, check https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html