diff --git a/CaptchaObject.php b/CaptchaObject.php
index 119bd9c..3f7e944 100644
--- a/CaptchaObject.php
+++ b/CaptchaObject.php
@@ -6,7 +6,7 @@ class CaptchaObject
 {
     public $captchaId;
     public $captchaImageData;
-    public $captchaImageAudio;
+    public $captchaAudioData;
     public $creationTime;
     public $code;
     public $code_display;
diff --git a/StorageAdapter/AdapterInterface.php b/StorageAdapter/AdapterInterface.php
index eccc7a7..4bc69ab 100644
--- a/StorageAdapter/AdapterInterface.php
+++ b/StorageAdapter/AdapterInterface.php
@@ -2,6 +2,8 @@
 
 namespace Securimage\StorageAdapter;
 
+use Securimage\CaptchaObject;
+
 interface AdapterInterface
 {
     /**
@@ -25,7 +27,7 @@ public function storeAudioData($captchaId, $audioData);
      *
      * @param string $captchaId The captcha ID to fetch info for
      * @param int    $what      What info to retrieve (e.g. code, image data, all)
-     * @return mixed false on failure, captcha info otherwise
+     * @return ?CaptchaObject NULL on failure, captcha info otherwise
      */
     public function get($captchaId, $what = null);
 
diff --git a/StorageAdapter/Mysqli.php b/StorageAdapter/Mysqli.php
index 6879c1c..9fc7e87 100644
--- a/StorageAdapter/Mysqli.php
+++ b/StorageAdapter/Mysqli.php
@@ -50,7 +50,7 @@ public function get($captchaId, $what = null)
             $info->code              = $code['code'];
             $info->code_display      = $code['code_display'];
             $info->creationTime      = (int)$code['created'];
-            $info->captchaImageAudio = $code['audio_data'];
+            $info->captchaAudioData = $code['audio_data'];
 
             return $info;
         }
diff --git a/StorageAdapter/PDO.php b/StorageAdapter/PDO.php
index 4141cc1..21bf598 100644
--- a/StorageAdapter/PDO.php
+++ b/StorageAdapter/PDO.php
@@ -51,7 +51,7 @@ public function get($captchaId, $what = null)
             $info->code              = $code['code'];
             $info->code_display      = $code['code_display'];
             $info->creationTime      = (int)$code['created'];
-            $info->captchaImageAudio = $code['audio_data'];
+            $info->captchaAudioData = $code['audio_data'];
 
             return $info;
         }
diff --git a/StorageAdapter/Session.php b/StorageAdapter/Session.php
index b43aad9..2ebdf33 100644
--- a/StorageAdapter/Session.php
+++ b/StorageAdapter/Session.php
@@ -20,8 +20,7 @@ public function __construct($options = null)
     public function store($captchaId, $captchaInfo)
     {
         if ((function_exists('session_status') && PHP_SESSION_ACTIVE == session_status()) || session_id() != '') {
-            $_SESSION['securimage_data'][$captchaId] = $captchaInfo;
-
+            $_SESSION['securimage_data'][$captchaId] = serialize($captchaInfo);
             return true;
         }
 
@@ -30,20 +29,24 @@ public function store($captchaId, $captchaInfo)
 
     public function storeAudioData($captchaId, $audioData)
     {
-        if (isset($_SESSION['securimage_data'][$captchaId]) &&
-            $_SESSION['securimage_data'][$captchaId] instanceof \Securimage\CaptchaObject
-        ) {
-            $_SESSION['securimage_data'][$captchaId]->captchaAudioData = $audioData;
-            return true;
+        $info = $this->get($captchaId);
+        if ($info === null) {
+            return false;
         }
 
-        return false;
+        $info->captchaAudioData = $audioData;
+        $this->store($captchaId, $info);
+        return true;
     }
 
-    public function get($captchaId, $what = null)
+    public function get($captchaId, $what = null): ?\Securimage\CaptchaObject
     {
         if (isset($_SESSION['securimage_data'][$captchaId])) {
-            return $_SESSION['securimage_data'][$captchaId];
+            $info = unserialize($_SESSION['securimage_data'][$captchaId]);
+            if (!($info instanceof \Securimage\CaptchaObject)) {
+                return null;
+            }
+            return $info;
         }
 
         return null;
diff --git a/WavFile.php b/WavFile.php
index f1180a5..4c245e5 100644
--- a/WavFile.php
+++ b/WavFile.php
@@ -1701,7 +1701,10 @@ public function filter($filters, $blockOffset = 0, $numBlocks = null)
 
                 /************* DEGRADE FILTER *******************/
                 if ($filter_degrade) {
-                    $sampleFloat += rand(1000000 * ($degrade_quality - 1), 1000000 * (1 - $degrade_quality)) / 1000000;
+                    $sampleFloat += rand(
+                        round(1000000 * ($degrade_quality - 1)),
+                        round(1000000 * (1 - $degrade_quality))
+                    ) / 1000000;
                 }
 
                 /************* VOLUME FILTER *******************/
diff --git a/securimage.php b/securimage.php
index d30d976..1b5a2e2 100644
--- a/securimage.php
+++ b/securimage.php
@@ -46,6 +46,8 @@
  *
  */
 
+use Securimage\StorageAdapter\AdapterInterface;
+
 
 /**
  * Securimage CAPTCHA Class.
@@ -614,7 +616,12 @@ class Securimage
      *
      * @var string
      */
-    protected $captcha_code;
+    protected $code_entered;
+
+    /**
+     * @var string
+     */
+    protected $correct_code;
 
     /**
      * Time (in seconds) that the captcha was solved in (correctly or incorrectly).
@@ -643,9 +650,9 @@ class Securimage
     /**
      * List of storage adapters for persisting captcha data
      *
-     * @var array Array of one or more storage adapters
+     * @var list<AdapterInterface> Array of one or more storage adapters
      */
-    protected $storage_adapters = array();
+    protected $storage_adapters = [];
 
     /**
      * Flag indicating whether or not HTTP headers will be sent when outputting
@@ -683,6 +690,11 @@ class Securimage
      */
     protected $gdsignaturecolor;
 
+    /**
+     * @var int
+     */
+    protected $gdnoisecolor;
+
     /**
      * Create a new securimage object, pass options to set in the constructor.
      *
@@ -1375,7 +1387,7 @@ public function outputAudioFile($format = null)
                 require_once dirname(__FILE__) . '/WavFile.php';
                 $audio = $this->getAudibleCode();
 
-                if (strtolower($format) == 'mp3') {
+                if (!empty($format) && strtolower($format) === 'mp3') {
                     $audio = $this->wavToMp3($audio);
                 }
 
@@ -1451,7 +1463,7 @@ public function rangeDownload($audio)
         $audioLength = $size = strlen($audio);
 
         if (isset($_SERVER['HTTP_RANGE'])) {
-            list( , $range) = explode('=', $_SERVER['HTTP_RANGE']); // bytes=byte-range-set
+            [ , $range] = explode('=', $_SERVER['HTTP_RANGE']); // bytes=byte-range-set
             $range = trim($range);
 
             if (strpos($range, ',') !== false) {
@@ -1981,11 +1993,11 @@ protected function distortedCopy()
         $py       = array(); // y coordinates of poles
         $rad      = array(); // radius of distortion from pole
         $amp      = array(); // amplitude
-        $x        = ($this->image_width / 4); // lowest x coordinate of a pole
+        $x        = round($this->image_width / 4); // lowest x coordinate of a pole
         $maxX     = $this->image_width - $x;  // maximum x coordinate of a pole
-        $dx       = mt_rand($x / 10, $x);     // horizontal distance between poles
+        $dx       = mt_rand(round($x / 10), $x);     // horizontal distance between poles
         $y        = mt_rand(20, $this->image_height - 20);  // random y coord
-        $dy       = mt_rand(20, $this->image_height * 0.7); // y distance
+        $dy       = mt_rand(20, round($this->image_height * 0.7, 0)); // y distance
         $minY     = 20;                                     // minimum y coordinate
         $maxY     = $this->image_height - 20;               // maximum y cooddinate
 
@@ -2018,7 +2030,7 @@ protected function distortedCopy()
                     if ($r > $rad[$i]) {
                         continue;
                     }
-                    $rscale = $amp[$i] * sin(3.14 * $r / $rad[$i]);
+                    $rscale = round($amp[$i] * sin(3.14 * $r / $rad[$i]));
                     $x += $dx * $rscale;
                     $y += $dy * $rscale;
                 }
@@ -2043,11 +2055,11 @@ protected function drawLines()
         for ($line = 0; $line < $this->num_lines; ++ $line) {
             $x = $this->image_width * (1 + $line) / ($this->num_lines + 1);
             $x += (0.5 - $this->frand()) * $this->image_width / $this->num_lines;
-            $y = mt_rand($this->image_height * 0.1, $this->image_height * 0.9);
+            $y = mt_rand(floor($this->image_height * 0.1), floor($this->image_height * 0.9));
 
             $theta = ($this->frand() - 0.5) * M_PI * 0.33;
             $w = $this->image_width;
-            $len = mt_rand($w * 0.4, $w * 0.7);
+            $len = mt_rand(round($w * 0.4), round($w * 0.7));
             $lwid = mt_rand(0, 2);
 
             $k = $this->frand() * 0.6 + 0.2;
@@ -2065,8 +2077,8 @@ protected function drawLines()
             $ldy = round($dx * $lwid);
 
             for ($i = 0; $i < $n; ++ $i) {
-                $x = $x0 + $i * $dx + $amp * $dy * sin($k * $i * $step + $phi);
-                $y = $y0 + $i * $dy - $amp * $dx * sin($k * $i * $step + $phi);
+                $x = round($x0 + $i * $dx + $amp * $dy * sin($k * $i * $step + $phi));
+                $y = round($y0 + $i * $dy - $amp * $dx * sin($k * $i * $step + $phi));
                 imagefilledrectangle($this->im, $x, $y, $x + $lwid, $y + $lwid, $this->gdlinecolor);
             }
         }
@@ -2461,19 +2473,18 @@ protected function saveAudioData($data, $captchaId)
 
     /**
      * Gets audio file contents from the session or database
-     *
-     * @return string|boolean Audio contents on success, or false if no audio found in session or DB
+     * @return ?string Audio contents on success, or NULL if no audio found in session or DB
      */
     protected function getAudioData($captchaId)
     {
         foreach($this->storage_adapters as $adapter) {
             $info = $adapter->get($captchaId);
-            if ($info && !empty($info->captchaImageAudio)) {
-                return $info->captchaImageAudio;
+            if ($info && !empty($info->captchaAudioData)) {
+                return $info->captchaAudioData;
             }
         }
 
-        return false;
+        return null;
     }
 
     /**