replace <img src="abc.png" alt="abc"> to <%= image_tag 'abc.png', alt: 'abc' %>

replace_img_to_image_tag_helper.rb

# usage:
# ruby replace_img_to_image_tag_helper.rb [REPLACED_FILE]

require 'nokogiri'

xhtml = true

content = open(ARGV[0]) { |f| f.read }.gsub(/\r\n?/, "\n").gsub("\t", '  ')
doc = Nokogiri::HTML(content)

doc.css('img').each do |img|
  attrs = img.attributes
  attrs['alt'] ||= ''
  src = attrs.delete('src')

  args = ["'#{ img['src'].sub(%r!^/?images/!, '') }'"]
  args += attrs.map { |k, v| %!#{ k }: '#{ v }'! }
  erb = "ERBBEGINESCAPE::::::::= image_tag #{ args * ', ' } ERBENDESCAPE::::::::"

  img.swap erb
end

puts doc.send(xhtml ? :to_xhtml : :to_html).
  gsub('ERBBEGINESCAPE::::::::', '<%').
  gsub('ERBENDESCAPE::::::::', '%>')