Captcha CODE not displayed

Hi there,
We have used CB Captcha on our CB Registration Form for years:
www.beautyontrial.co.uk/registration/registers
For the last few days, we have noticed that the image CODE hasn't been displayed on the form.
- see attached screenshot -
We have tested the same on Google, Safari and Chrome with PC and smartphones.
Since this field is required, new visitors aren't able to register.
How can we resolve this issue?

CB Captcha has long been deprecated. I've no idea if it still works. It has been replaced by CB AntiSpam, which is working fine. If it suddenly stopped working it suggests a change was made on your site or your host to break it.

Hi krileon,
Thank you for your reply.

Is CB Captcha named antispam_captcha?
If yes, we have disabled this field to remove it from our registration form:
www.beautyontrial.co.uk/register

CB AntiSpam is still published.
Would you recommend installing a Captcha field on our registration form even with CB AntiSpam activated?
If yes, how to proceed?

CB AntiSpam provides captcha through its antispam_captcha field, yes. Maybe it's an issue with being out of date. I don't know. Obviously something has changed either on your install or server to break it as plugins don't just suddenly stop working. CB AntiSpam plugin it self should be public and published; the captcha field can't work otherwise.