diff --git a/CHANGELOG b/CHANGELOG
index 7791b8c..2cab94b 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,6 @@
 = Version 0.4
   * Added project generator (ace-gen).
+  * Fixed filter for image thumbnails.
 
 = Version 0.3
   * Added LazyRendering mixin.
diff --git a/lib/ace/filters/image_thumbnailer.rb b/lib/ace/filters/image_thumbnailer.rb
index e952c17..b4d5774 100644
--- a/lib/ace/filters/image_thumbnailer.rb
+++ b/lib/ace/filters/image_thumbnailer.rb
@@ -3,37 +3,59 @@
 require "ace/filters"
 require "nokogiri"
 
+# <thumbnail src="assets/img/motivation-sheet.jpg" />
+# <thumbnail src="assets/img/motivation-sheet.jpg" size="550" />
+# <thumbnail src="assets/img/motivation-sheet.jpg" size="550x20" />
+
+# TODO:
+# class Post < Ace::Item
+#   before Ace::ImageThumbnailerFilter, default_thumb_size: 550
+# end
 module Ace
   class ImageThumbnailerFilter < Filter
-    def thumb_name(filename)
-      filename.gsub(/\.([^\.]*)$/, '_thumb.\1')
+    def thumb_path(file_name)
+      @file_name ||= file_name
+      @thumb_path ||= file_name.gsub(/\.([^\.]*)$/, '_thumb.\1')
     end
 
-    def thumbnail_nodeset(filename, doc)
-      a = Nokogiri::XML::Node.new 'a', doc
-      img = Nokogiri::XML::Node.new 'img', doc
-      a.set_attribute('href', filename)
-      img.set_attribute('src', thumb_name(filename))
-      img.parent = a
-      a
+    def thumb_server_path
+      @thumb_path.sub("content", "")
     end
-    
-    def make_thumbnail_image(filename, size)
-      size ||= 20   # default size
-      cmd = "convert content#{filename} -resize #{size} content#{thumb_name(filename)}"
-      warn "~ make thumbnail with '#{cmd}'"
-      system(cmd)
-      raise "Error when converting image 'content#{filename}'" if $?.to_i != 0
+
+    def original_image_server_path
+      @file_name.sub("content", "")
+    end
+
+    def thumbnail_nodeset(file_name, doc)
+      link  = Nokogiri::XML::Node.new("a", doc)
+      image = Nokogiri::XML::Node.new("img", doc)
+      link.set_attribute("href", original_image_server_path)
+      image.set_attribute("src", thumb_server_path)
+      image.parent = link
+      return link
     end
 
     def call(item, content)
-      puts item.inspect
+      puts "~ [THUMB] #{item.original_path}"
       doc = Nokogiri::HTML(content)
       doc.css("thumbnail").each do |thumb|
-        make_thumbnail_image thumb[:src], thumb[:size]
-        thumb.replace thumbnail_nodeset(thumb[:src], doc)
+        original_file = "content/#{thumb[:src]}"
+        generate_thumbnail(original_file, thumb[:size] || 550)
+        thumb.replace(thumbnail_nodeset(original_file, doc))
       end
       doc.to_s
     end
+
+    private
+    def generate_thumbnail(file_name, size)
+      unless File.exist?(thumb_path(file_name))
+        command = "convert #{file_name} -resize #{size} #{thumb_path(file_name)}"
+        warn "~ $ #{command}"
+        system(command)
+        raise "Error when converting image '#{file_name}'" if $?.to_i != 0
+      else
+        warn "~ File #{thumb_path(file_name)} already exists."
+      end
+    end
   end
 end
diff --git a/lib/ace/version.rb b/lib/ace/version.rb
index 9337881..ea8e5f2 100644
--- a/lib/ace/version.rb
+++ b/lib/ace/version.rb
@@ -1,5 +1,5 @@
 # encoding: utf-8
 
 module Ace
-  VERSION = "0.4.1"
+  VERSION = "0.4.2"
 end