www.moparisthebest.com/plugins/image_tag.rb

# Title: Simple Image tag for Jekyll
# Author: Brandon Mathis http://brandonmathis.com
# Description: Easily output images with optional class names and title/alt attributes
#
# Syntax {% image [class name(s)] url [title text] %}
#
# Example:
# {% ima left half http://site.com/images/ninja.png Ninja Attack! %}
#
# Output:
# <image class='left' src="http://site.com/images/ninja.png" title="Ninja Attack!" alt="Ninja Attack!">
#

module Jekyll

  class ImageTag < Liquid::Tag
    @img = nil
    @title = nil
    @class = ''

    def initialize(tag_name, markup, tokens)
      if markup =~ /(\S.*\s+)?(https?:\/\/|\/)(\S+)(\s+.+)?/i
        @class = $1
        @img = $2 + $3
        @title = $4
      end
      super
    end

    def render(context)
      output = super
      if @img
        "<img class='#{@class}' src='#{@img}' alt='#{@title}' title='#{@title}'>"
      else
        "Error processing input, expected syntax: {% img [class name(s)] /url/to/image [title text] %}"
      end
    end
  end
end

Liquid::Template.register_tag('img', Jekyll::ImageTag)