Index: app/helpers/application_helper.rb
===================================================================
--- app/helpers/application_helper.rb	(revision 17198)
+++ app/helpers/application_helper.rb	(working copy)
@@ -1407,10 +1407,12 @@
       end
       if email.present?
         gravatar(email.to_s.downcase, options) rescue nil
-      else
+      elsif user.is_a?(AnonymousUser)
         image_tag 'anonymous.png',
                   GravatarHelper::DEFAULT_OPTIONS
                     .except(:default, :rating, :ssl).merge(options)
+      else
+        nil
       end
     else
       ''
Index: test/helpers/application_helper_test.rb
===================================================================
--- test/helpers/application_helper_test.rb	(revision 17198)
+++ test/helpers/application_helper_test.rb	(working copy)
@@ -1302,7 +1302,6 @@
   end
 
   def test_avatar_enabled
-    tag_for_anonymous_re = %r{src="/images/anonymous.png(\?\d+)?"}
     with_settings :gravatar_enabled => '1' do
       assert avatar(User.find_by_mail('jsmith@somenet.foo')).include?(Digest::MD5.hexdigest('jsmith@somenet.foo'))
       assert avatar('jsmith <jsmith@somenet.foo>').include?(Digest::MD5.hexdigest('jsmith@somenet.foo'))
@@ -1314,10 +1313,12 @@
       # The default class of the img tag should be gravatar
       assert avatar('jsmith <jsmith@somenet.foo>').include?('class="gravatar"')
       assert !avatar('jsmith <jsmith@somenet.foo>', :class => 'picture').include?('class="gravatar"')
-      assert_match tag_for_anonymous_re, avatar('jsmith')
-      assert_match tag_for_anonymous_re, avatar(nil)
+      assert_nil avatar('jsmith')
+      assert_nil avatar(nil)
       # Avatar for anonymous user
-      assert_match tag_for_anonymous_re, avatar(User.anonymous)
+      assert_match %r{src="/images/anonymous.png(\?\d+)?"}, avatar(User.anonymous)
+      # No avatar for groups
+      assert_nil avatar(Group.first)
     end
   end