addressed issue #1324 for URL escaping of (, ), [, and ] characters.

lib/paperclip/url_generator.rb

@@ -58,7 +58,7 @@ module Paperclip
     end
 
     def escape_url(url)
-      (url.respond_to?(:escape) ? url.escape : URI.escape(url)).gsub(/(\/.+)\?(.+\.)/, '\1%3F\2')
+      (url.respond_to?(:escape) ? url.escape : URI.escape(url)).gsub(/(\/.+)\?(.+\.)/, '\1%3F\2').gsub(/\(/, '%28').gsub(/\)/, '%29').gsub(/\[/, '%5B').gsub(/\]/, '%5D')
     end
   end
 end

spec/paperclip/url_generator_spec.rb

@@ -183,4 +183,17 @@ describe Paperclip::UrlGenerator do
     assert mock_interpolator.has_interpolated_pattern?(expected),
       "expected the interpolator to be passed #{expected.inspect} but it wasn't"
   end
+
+  it "should be able to escape (, ), [, and ]." do
+    expected = "the(expected)result[]"
+    mock_attachment = MockAttachment.new
+    mock_interpolator = MockInterpolator.new(result: expected)
+    options = { interpolator: mock_interpolator }
+    url_generator = Paperclip::UrlGenerator.new(mock_attachment, options)
+    def url_generator.respond_to(params)
+      false if params == :escape
+    end
+    result = url_generator.for(:style_name, {escape: true})
+    assert_equal "the%28expected%29result%5B%5D", result
+  end
 end