diff --git a/lib/redcloth3.rb b/lib/redcloth3.rb
index f9c9054..b96ee7a 100644
--- a/lib/redcloth3.rb
+++ b/lib/redcloth3.rb
@@ -165,6 +165,7 @@
 #  class RedCloth::Textile.new( str )
 
 class RedCloth3 < String
+    include Redmine::Helpers::URL
 
     VERSION = '3.0.4'
     DEFAULT_RULES = [:textile, :markdown]
@@ -960,6 +961,8 @@ class RedCloth3 < String
             href, alt_title = check_refs( href ) if href
             url, url_title = check_refs( url )
 
+            return m unless uri_with_safe_scheme?(url)
+
             out = ''
             out << "<a#{ shelve( " href=\"#{ href }\"" ) }>" if href
             out << "<img#{ shelve( atts ) } />"
diff --git a/lib/redmine/wiki_formatting/markdown/formatter.rb b/lib/redmine/wiki_formatting/markdown/formatter.rb
index 2d6f665..4afbc2f 100644
--- a/lib/redmine/wiki_formatting/markdown/formatter.rb
+++ b/lib/redmine/wiki_formatting/markdown/formatter.rb
@@ -43,6 +43,12 @@ module Redmine
             "<pre>" + CGI.escapeHTML(code) + "</pre>"
           end
         end
+
+        def image(link, title, alt_text)
+          return unless uri_with_safe_scheme?(link)
+
+          tag('img', :src => link, :alt => alt_text || "", :title => title)
+        end
       end
 
       class Formatter