search_image_tag_in_md.rb

#!/usr/bin/ruby

require 'find'

@image = /^[!][\[]*/

i = 1
Find.find('.') {|fname| 
  if ( File.extname(fname) == '.md' || File.extname(fname) == '.markdown' )

    File.open(fname, "r") { |original|
      original.each_line {|line|
        if @image.match(line.chomp)
          puts "#{i}: #{line.chomp}" 
          i += 1
        end
      }
    }
  end
}