Thanks for the response. It turns out it was my ad blocker software interfering with the embedding. By disabling the adblocker, the problem solved itself.
If a plugin won’t work with other plugins, that means it is a serious flaw in the plugin’s design. Feel free to disagree on my star-rating all you like. If you’re involved with the plugin’s design, look at improving it and I may reconsider my rating, but an unusable plugin isn’t going to get a good rating.
For myself, I eventually gave up and switched to something that worked without me needing to tinker with it.
Don’t get me wrong here – I’m not overly bothered about mucking around in the PHP, Javascript, or whatever I need to muck around in to make things work – I’m personally writing the Most Amazing WordPress Theme You’ve Ever Seen – (a subjective and biased opinion) – but there are so many Captcha options out there that work, I really couldn’t be bothered messing around with this one.