I have a self-hosted matrix-synapse server up and running on a Debian linux server, but before I open it up I want to at least get a captcha service in place to reduce spamming. The only module I've seen to handle this function appears to require setting up a Google recaptcha though, however I would prefer to keep all of this entirely self-contained for the privacy of my users. Can anyone recommend a module that allows for a local captcha option? For that matter, can anyone also recommend a captcha system that is pretty straightforward to set up (which is compatible with matrix-synapse) and uses basic preinstalled code bases like perl or python?

And while I'm here, I would also like to provide the option of registering with an email address, but I'm having trouble finding any clear how-to pages on this. Seems like that function might be built directly in to matrix-synapse but I'm just not finding anything helpful. Any suggestions?

I'm fairly new to matrix in general, but I have an initial setup running with the homeserver, Element web page, and an IRC bridge, so if I can just nail down the validation part of registrations I'll have what I think is a good starting point to launch from.