diff --git a/system/helpers/captcha_helper.php b/system/helpers/captcha_helper.php
index 57ef9e2..3aac14d 100644
--- a/system/helpers/captcha_helper.php
+++ b/system/helpers/captcha_helper.php
@@ -80,7 +80,7 @@
 		$current_dir = @opendir($img_path);
 		while ($filename = @readdir($current_dir))
 		{
-			if (strpos($filename, ".jpg") !== FALSE && (str_replace('.jpg', '', $filename) + $expiration) < $now)
+			if (substr($filename, -4) === '.jpg' && (str_replace('.jpg', '', $filename) + $expiration) < $now)
 			{
 				@unlink($img_path.$filename);
 			}