diff --git a/lib/paperclip.rb b/lib/paperclip.rb
index 3fe6fdb3d..6effec6e7 100644
--- a/lib/paperclip.rb
+++ b/lib/paperclip.rb
@@ -58,6 +58,8 @@
 require 'mime/types'
 require 'logger'
 require 'cocaine'
+require 'mimemagic'
+require 'mimemagic/overlay'
 
 require 'paperclip/railtie' if defined?(Rails)
 
diff --git a/lib/paperclip/attachment.rb b/lib/paperclip/attachment.rb
index 47e95f0ce..2913ec68b 100644
--- a/lib/paperclip/attachment.rb
+++ b/lib/paperclip/attachment.rb
@@ -147,7 +147,8 @@ def url(style_name = default_style, options = {})
     def default_options
       {
         :timestamp => @options[:use_timestamp],
-        :escape => @options[:escape_url]
+        :escape => @options[:escape_url],
+        :url_filter => Paperclip.options[:url_filter]
       }
     end
 
diff --git a/lib/paperclip/content_type_detector.rb b/lib/paperclip/content_type_detector.rb
index ff286213b..ccab48774 100644
--- a/lib/paperclip/content_type_detector.rb
+++ b/lib/paperclip/content_type_detector.rb
@@ -33,7 +33,7 @@ def detect
       elsif calculated_type_matches.any?
         calculated_type_matches.first
       else
-        type_from_file_command || SENSIBLE_DEFAULT
+        type_from_file_contents || SENSIBLE_DEFAULT
       end.to_s
     end
 
@@ -54,11 +54,26 @@ def possible_types
     end
 
     def calculated_type_matches
-      possible_types.select{|content_type| content_type == type_from_file_command }
+      possible_types.select do |content_type|
+        content_type == type_from_file_contents
+      end
+    end
+
+    def type_from_file_contents
+      type_from_mime_magic || type_from_file_command
+    rescue Errno::ENOENT => e
+      Paperclip.log("Error while determining content type: #{e}")
+      SENSIBLE_DEFAULT
     end
 
     def type_from_file_command
-      @type_from_file_command ||= FileCommandContentTypeDetector.new(@filename).detect
+      @type_from_file_command ||=
+        FileCommandContentTypeDetector.new(@filename).detect
+    end
+
+    def type_from_mime_magic
+      @type_from_mime_magic ||=
+        MimeMagic.by_magic(File.open(@filename)).try(:type)
     end
   end
 end
diff --git a/lib/paperclip/file_command_content_type_detector.rb b/lib/paperclip/file_command_content_type_detector.rb
index a711597fe..6623484c2 100644
--- a/lib/paperclip/file_command_content_type_detector.rb
+++ b/lib/paperclip/file_command_content_type_detector.rb
@@ -13,20 +13,18 @@ def detect
     private
 
     def type_from_file_command
+      # On BSDs, `file` doesn't give a result code of 1 if the file doesn't exist.
       type = begin
-        # On BSDs, `file` doesn't give a result code of 1 if the file doesn't exist.
-        Paperclip.run("file", "-b --mime :file", :file => @filename)
-      rescue Cocaine::CommandLineError => e
-        Paperclip.log("Error while determining content type: #{e}")
-        SENSIBLE_DEFAULT
-      end
+               Paperclip.run("file", "-b --mime :file", file: @filename)
+             rescue Cocaine::CommandLineError => e
+               Paperclip.log("Error while determining content type: #{e}")
+               SENSIBLE_DEFAULT
+             end
 
       if type.nil? || type.match(/\(.*?\)/)
         type = SENSIBLE_DEFAULT
       end
       type.split(/[:;\s]+/)[0]
     end
-
   end
 end
-
diff --git a/lib/paperclip/interpolations.rb b/lib/paperclip/interpolations.rb
index 210886a38..62d5bf60b 100644
--- a/lib/paperclip/interpolations.rb
+++ b/lib/paperclip/interpolations.rb
@@ -51,7 +51,7 @@ def filename attachment, style_name
     RIGHT_HERE = "#{__FILE__.gsub(%r{\A\./}, "")}:#{__LINE__ + 3}"
     def url attachment, style_name
       raise Errors::InfiniteInterpolationError if caller.any?{|b| b.index(RIGHT_HERE) }
-      attachment.url(style_name, :timestamp => false, :escape => false)
+      attachment.url(style_name, :timestamp => false, :escape => false, :signing_validity => :internal)
     end
 
     # Returns the timestamp as defined by the <attachment>_updated_at field
diff --git a/lib/paperclip/url_generator.rb b/lib/paperclip/url_generator.rb
index 31e0fd40b..c8075d3e2 100644
--- a/lib/paperclip/url_generator.rb
+++ b/lib/paperclip/url_generator.rb
@@ -8,15 +8,22 @@ def initialize(attachment, attachment_options)
     end
 
     def for(style_name, options)
-      escape_url_as_needed(
-        timestamp_as_needed(
-          @attachment_options[:interpolator].interpolate(most_appropriate_url, @attachment, style_name),
-          options
-      ), options)
+      run_filter(
+        escape_url_as_needed(
+          timestamp_as_needed(
+            @attachment_options[:interpolator].interpolate(most_appropriate_url, @attachment, style_name),
+            options
+          ), options
+        ), options
+      )
     end
 
     private
 
+    def run_filter(url, options)
+      return url if @attachment.original_filename.nil?
+      options[:url_filter].call(url, options)
+    end
     # This method is all over the place.
     def default_url
       if @attachment_options[:default_url].respond_to?(:call)
diff --git a/paperclip.gemspec b/paperclip.gemspec
index ed6a0d429..673d6dfb6 100644
--- a/paperclip.gemspec
+++ b/paperclip.gemspec
@@ -26,6 +26,7 @@ Gem::Specification.new do |s|
   s.add_dependency('activesupport', '>= 3.0.0')
   s.add_dependency('cocaine', '~> 0.5.3')
   s.add_dependency('mime-types')
+  s.add_dependency('mimemagic', '0.3.3')
 
   s.add_development_dependency('activerecord', '>= 3.0.0')
   s.add_development_dependency('shoulda')