2 files changed, 14 insertions, 2 deletions
diff --git a/actionpack/lib/action_view/helpers/asset_tag_helper.rb b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
index 626cc7d3b0..25426a5547 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helper.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
@@ -620,7 +620,10 @@ module ActionView
         options.symbolize_keys!
 
         src = options[:src] = path_to_image(source)
-        options[:alt] = options.fetch(:alt){ File.basename(src, '.*').capitalize }
+
+        unless src =~ /^cid:/
+          options[:alt] = options.fetch(:alt){ File.basename(src, '.*').capitalize }
+        end
 
         if size = options.delete(:size)
           options[:width], options[:height] = size.split("x") if size =~ %r{^\d+x\d+$}
@@ -754,7 +757,7 @@ module ActionView
         end
 
         def is_uri?(path)
-          path =~ %r{^[-a-z]+://}
+          path =~ %r{^[-a-z]+://|^cid:}
         end
 
         # Pick an asset host for this source. Returns +nil+ if no host is set,
diff --git a/actionpack/test/template/asset_tag_helper_test.rb b/actionpack/test/template/asset_tag_helper_test.rb
index b6a6f52876..633641514e 100644
--- a/actionpack/test/template/asset_tag_helper_test.rb
+++ b/actionpack/test/template/asset_tag_helper_test.rb
@@ -404,6 +404,15 @@ class AssetTagHelperTest < ActionView::TestCase
     assert_equal %(<img alt="Rails" src="#{expected_path}" />), image_tag("rails.png")
   end
 
+  def test_image_tag_interpreting_email_cid_correctly
+    # An inline image has no need for an alt tag to be automatically generated from the cid:
+    assert_equal '<img src="cid:thi%25%25sis@acontentid" />', image_tag("cid:thi%25%25sis@acontentid")
+  end
+
+  def test_image_tag_interpreting_email_adding_optional_alt_tag
+    assert_equal '<img alt="Image" src="cid:thi%25%25sis@acontentid" />', image_tag("cid:thi%25%25sis@acontentid", :alt => "Image")
+  end
+
   def test_timebased_asset_id_with_relative_url_root
     @controller.config.relative_url_root = "/collaboration/hieraki"
     expected_time = File.stat(File.expand_path(File.dirname(__FILE__) + "/../fixtures/public/images/rails.png")).mtime.to_i.to_s