diff --git a/proxy/data.go b/proxy/data.go
index 76fb0cd..bf184fd 100644
--- a/proxy/data.go
+++ b/proxy/data.go
@@ -16,6 +16,7 @@
 package proxy
 
 import (
+	"bytes"
 	"fmt"
 	"net/url"
 	"strconv"
@@ -41,7 +42,21 @@ type Options struct {
 }
 
 func (o Options) String() string {
-	return fmt.Sprintf("%vx%v", o.Width, o.Height)
+	buf := new(bytes.Buffer)
+	fmt.Fprintf(buf, "%vx%v", o.Width, o.Height)
+	if o.Fit {
+		buf.WriteString(",fit")
+	}
+	if o.Rotate != 0 {
+		fmt.Fprintf(buf, ",r%d", o.Rotate)
+	}
+	if o.FlipVertical {
+		buf.WriteString(",fv")
+	}
+	if o.FlipHorizontal {
+		buf.WriteString(",fh")
+	}
+	return buf.String()
 }
 
 func ParseOptions(str string) *Options {
diff --git a/proxy/data_test.go b/proxy/data_test.go
new file mode 100644
index 0000000..0a6ee81
--- /dev/null
+++ b/proxy/data_test.go
@@ -0,0 +1,36 @@
+// Copyright 2013 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package proxy
+
+import "testing"
+
+func TestOptions_String(t *testing.T) {
+	tests := []struct {
+		Options *Options
+		String  string
+	}{
+		{emptyOptions, "0x0"},
+		{
+			&Options{1, 2, true, 90, true, true},
+			"1x2,fit,r90,fv,fh",
+		},
+	}
+
+	for i, tt := range tests {
+		if got, want := tt.Options.String(), tt.String; got != want {
+			t.Errorf("%d. Options.String returned %v, want %v", i, got, want)
+		}
+	}
+}