--- a/helper.php	2013-04-29 06:50:38.000000000 +0900
+++ b/helper.php	2013-05-05 19:55:44.000000000 +0900
@@ -88,7 +88,7 @@
                 }
                 break;
         }
-        $out .= ' <input type="text" size="5" maxlength="5" name="'.$this->field_in.'" class="edit" /> ';
+        $out .= ' <input type="text" size="10" maxlength="10" name="'.$this->field_in.'" class="edit" /> ';
 
         // add honeypot field
         $out .= '<label class="no">Please keep this field empty: <input type="text" name="'.$this->field_hp.'" /></label>';
@@ -150,11 +150,18 @@
         $numbers = md5($rand * $fixed); // combine both values
 
         // now create the letters
+/*
         $code = '';
         for($i=0;$i<10;$i+=2){
             $code .= chr(floor(hexdec($numbers[$i].$numbers[$i+1])/10) + 65);
         }
-
+*/
+        $strTable = 'あいうえおかきくけこさしすせそたちつてとなにぬねのはひふへほまみむめもやゐゆゑよらりるれろわをん';
+        $strLength = mb_strlen($strTable);
+        $code = '';
+        for ($i=0;$i<10;$i+=2){
+            $code .= mb_substr($strTable, hexdec($numbers[$i].$numbers[$i+1])%$strLength, 1);
+        }
         return $code;
     }
 
@@ -203,7 +210,7 @@
         }
 
         // draw the letters
-        for ($i = 0; $i < strlen($text); $i++){
+        for ($i = 0; $i < mb_strlen($text); $i++){
             $font  = $fonts[array_rand($fonts)];
             $color = imagecolorallocate($img, rand(0, 100), rand(0, 100), rand(0, 100));
             $size  = rand(floor($h/1.8),floor($h*0.7));
@@ -213,7 +220,7 @@
             $cheight = $size + ($size*0.5);
             $y = floor($h / 2 + $cheight / 3.8);
 
-            imagettftext($img, $size, $angle, $x, $y, $color, $font, $text[$i]);
+            imagettftext($img, $size, $angle, $x, $y, $color, $font, mb_substr($text, $i, 1));
         }
 
         header("Content-type: image/png");