Yep this is a global option in /admin/settings/user#default-user-settings
0_1460524770594_Screen Shot 2016-04-13 at 06.16.41.png
Following the mention of Playthru here, I found another anti-spam tool that I think is better than Playthru. It's more user-friendly and looks really nice.
More about it at visualCaptcha. Demo of the Node implementation is available here. GitHub page is here.