diff --git a/phpBB/includes/ucp/ucp_register.php b/phpBB/includes/ucp/ucp_register.php
index 40b14a9b54..8ad37047cb 100644
--- a/phpBB/includes/ucp/ucp_register.php
+++ b/phpBB/includes/ucp/ucp_register.php
@@ -235,8 +235,10 @@ class ucp_register
 		// The CAPTCHA kicks in here. We can't help that the information gets lost on language change.
 		if ($config['enable_confirm'])
 		{
-			$captcha = $phpbb_container->get('captcha.factory')->get_instance($config['captcha_plugin']);
-			$captcha->init(CONFIRM_REG);
+			/** @var \phpbb\captcha\factory $captcha_factory */
+			$captcha_factory = $phpbb_container->get('captcha.factory');
+			$captcha = $captcha_factory->get_instance($config['captcha_plugin']);
+			$captcha->init(\phpbb\captcha\plugins\plugin_interface::CONFIRM_REGISTRATION);
 		}
 
 		$timezone = $config['board_timezone'];
@@ -426,7 +428,7 @@ class ucp_register
 				}
 
 				// Okay, captcha, your job is done.
-				if ($config['enable_confirm'] && isset($captcha))
+				if ($config['enable_confirm'])
 				{
 					$captcha->reset();
 				}
diff --git a/phpBB/phpbb/captcha/factory.php b/phpBB/phpbb/captcha/factory.php
index 2e75ce8667..971a7b2118 100644
--- a/phpBB/phpbb/captcha/factory.php
+++ b/phpBB/phpbb/captcha/factory.php
@@ -13,6 +13,9 @@
 
 namespace phpbb\captcha;
 
+use phpbb\captcha\plugins\legacy_wrapper;
+use phpbb\captcha\plugins\plugin_interface;
+
 class factory
 {
 	/**
@@ -41,11 +44,17 @@ class factory
 	* Return a new instance of a given plugin
 	*
 	* @param $name
-	* @return object|null
+	* @return plugin_interface
 	*/
-	public function get_instance($name)
+	public function get_instance($name): plugin_interface
 	{
-		return $this->container->get($name);
+		$captcha = $this->container->get($name);
+		if ($captcha instanceof plugin_interface)
+		{
+			return $captcha;
+		}
+
+		return new legacy_wrapper($name);
 	}
 
 	/**
diff --git a/phpBB/phpbb/captcha/plugins/legacy_wrapper.php b/phpBB/phpbb/captcha/plugins/legacy_wrapper.php
index 90ff01995b..bceb771800 100644
--- a/phpBB/phpbb/captcha/plugins/legacy_wrapper.php
+++ b/phpBB/phpbb/captcha/plugins/legacy_wrapper.php
@@ -17,6 +17,8 @@ class legacy_wrapper implements plugin_interface
 {
 	private $legacy_captcha;
 
+	private string $last_error;
+
 	public function __construct($legacy_captcha)
 	{
 		$this->legacy_captcha = $legacy_captcha;
@@ -72,11 +74,69 @@ class legacy_wrapper implements plugin_interface
 	 * @param int $type Type of captcha, should be one of the CONFIRMATION_* constants
 	 * @return void
 	 */
-	public function show(int $type): void
+	public function init(int $type): void
 	{
 		if (method_exists($this->legacy_captcha, 'init'))
 		{
 			$this->legacy_captcha->init($type);
 		}
 	}
-}
\ No newline at end of file
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function validate(array $request_data): bool
+	{
+		if (method_exists($this->legacy_captcha, 'validate'))
+		{
+			$error = $this->legacy_captcha->validate($request_data);
+			if ($error)
+			{
+				$this->last_error = $error;
+				return false;
+			}
+
+			return true;
+		}
+
+		return false;
+	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function is_solved(): bool
+	{
+		if (method_exists($this->legacy_captcha, 'is_solved'))
+		{
+			return $this->legacy_captcha->is_solved();
+		}
+
+		return false;
+	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function reset(): void
+	{
+		if (method_exists($this->legacy_captcha, 'reset'))
+		{
+			$this->legacy_captcha->reset();
+		}
+	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function get_attempt_count(): int
+	{
+		if (method_exists($this->legacy_captcha, 'get_attempt_count'))
+		{
+			return $this->legacy_captcha->get_attempt_count();
+		}
+
+		// Ensure this is deemed as too many attempts
+		return PHP_INT_MAX;
+	}
+}
diff --git a/phpBB/phpbb/captcha/plugins/plugin_interface.php b/phpBB/phpbb/captcha/plugins/plugin_interface.php
index 51c8d3d23d..9d0b0cb4de 100644
--- a/phpBB/phpbb/captcha/plugins/plugin_interface.php
+++ b/phpBB/phpbb/captcha/plugins/plugin_interface.php
@@ -15,16 +15,17 @@ namespace phpbb\captcha\plugins;
 
 interface plugin_interface
 {
-	const CONFIRMATION_REGISTRATION = 1;
-	const CONFIRMATION_LOGIN = 2;
+	const CONFIRM_REGISTRATION = 1;
+	const CONFIRM_LOGIN = 2;
 
-	const CONFIRMATION_POST = 3;
+	const CONFIRM_POST = 3;
 
-	const CONFIRMATION_REPORT = 4;
+	const CONFIRM_REPORT = 4;
 
 
 	/**
 	 * Check if the plugin is available
+	 *
 	 * @return bool True if the plugin is available, false if not
 	 */
 	public function is_available(): bool;
@@ -49,5 +50,34 @@ interface plugin_interface
 	 * @param int $type Type of captcha, should be one of the CONFIRMATION_* constants
 	 * @return void
 	 */
-	public function show(int $type): void;
+	public function init(int $type): void;
+
+	/**
+	 * Validate the captcha with the given request data
+	 *
+	 * @param array $request_data Request data for the captcha
+	 * @return bool True if request data was valid captcha reply, false if not
+	 */
+	public function validate(array $request_data): bool;
+
+	/**
+	 * Return whether captcha was solved
+	 *
+	 * @return bool True if captcha was solved, false if not
+	 */
+	public function is_solved(): bool;
+
+	/**
+	 * Reset captcha state, e.g. after checking if it's valid
+	 *
+	 * @return void
+	 */
+	public function reset(): void;
+
+	/**
+	 * Get attempt count for this captcha and user
+	 *
+	 * @return int Number of attempts
+	 */
+	public function get_attempt_count(): int;
 }
diff --git a/phpBB/posting.php b/phpBB/posting.php
index 63ca4fef97..988b7f03e2 100644
--- a/phpBB/posting.php
+++ b/phpBB/posting.php
@@ -455,8 +455,10 @@ if (!$is_authed || !empty($error))
 
 if ($config['enable_post_confirm'] && !$user->data['is_registered'])
 {
-	$captcha = $phpbb_container->get('captcha.factory')->get_instance($config['captcha_plugin']);
-	$captcha->init(CONFIRM_POST);
+	/** @var \phpbb\captcha\factory $captcha_factory */
+	$captcha_factory = $phpbb_container->get('captcha.factory');
+	$captcha = $captcha_factory->get_instance($config['captcha_plugin']);
+	$captcha->init(\phpbb\captcha\plugins\plugin_interface::CONFIRM_POST);
 }
 
 // Is the user able to post within this forum?
@@ -1600,7 +1602,7 @@ if ($submit || $preview || $refresh)
 			);
 			extract($phpbb_dispatcher->trigger_event('core.posting_modify_submit_post_after', compact($vars)));
 
-			if ($config['enable_post_confirm'] && !$user->data['is_registered'] && (isset($captcha) && $captcha->is_solved() === true) && ($mode == 'post' || $mode == 'reply' || $mode == 'quote'))
+			if ($config['enable_post_confirm'] && !$user->data['is_registered'] && $captcha->is_solved() === true && ($mode == 'post' || $mode == 'reply' || $mode == 'quote'))
 			{
 				$captcha->reset();
 			}