validates_attachment_content_type :image, :content_type => /^image\/(jpg|jpeg|pjpeg|png|x-png|gif)$/, :message => 'file type is not allowed (only jpeg/png/gif images)'
Rails Long Term Support
Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)
Prevents you from data breaches and liability risks