You have probably activated Prevent escaping CAPTCHA option.
This option registers the app as a device administrator in order to block turning off the phone when an alarm rings.
To uninstall the app, you have to unregister the app as device administrator first. This is usually done as follows:
- System settings >Location and Security > Device Administrator and deselect the admin which you want to uninstall.
- Now uninstall the application. If it still says you need to deactivate the application before uninstalling, you may need to Force Stop the application before uninstalling.