diff --git a/accounts_test.go b/accounts_test.go
index a369c3b..e7bc167 100644
--- a/accounts_test.go
+++ b/accounts_test.go
@@ -34,8 +34,6 @@ func TestAccountUpdate(t *testing.T) {
 	}
 }
 
-func String(v string) *string { return &v }
-
 func TestGetBlocks(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprintln(w, `[{"Username": "foo"}, {"Username": "bar"}]`)
diff --git a/helper.go b/helper.go
new file mode 100644
index 0000000..b606695
--- /dev/null
+++ b/helper.go
@@ -0,0 +1,36 @@
+package mastodon
+
+import (
+	"encoding/base64"
+	"net/http"
+	"os"
+)
+
+func Base64EncodeFileName(filename string) (string, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	return Base64Encode(file)
+}
+
+func Base64Encode(file *os.File) (string, error) {
+	fi, err := file.Stat()
+	if err != nil {
+		return "", err
+	}
+
+	d := make([]byte, fi.Size())
+	_, err = file.Read(d)
+	if err != nil {
+		return "", err
+	}
+
+	return "data:" + http.DetectContentType(d) +
+		";base64," + base64.StdEncoding.EncodeToString(d), nil
+}
+
+// String is a helper function to get the pointer value of a string.
+func String(v string) *string { return &v }
diff --git a/helper_test.go b/helper_test.go
new file mode 100644
index 0000000..a4a6429
--- /dev/null
+++ b/helper_test.go
@@ -0,0 +1,13 @@
+package mastodon
+
+import (
+	"testing"
+)
+
+func TestString(t *testing.T) {
+	s := "test"
+	sp := String(s)
+	if *sp != s {
+		t.Fatalf("want %q but %q", s, *sp)
+	}
+}