Hi
I had the same issue. ( NOP Version 3.70 ) . Rather foolishly tried to do this on a livesite and locked myself out.
I updated the following values in [Setting] table. I had to restart my website to enable changes.
captchasettings.enabled False
captchasettings.showonloginpage False
captchasettings.showonregistrationpage False
aptchasettings.showoncontactuspage False
captchasettings.showonemailwishlisttofriendpage False
captchasettings.showonemailproducttofriendpage False
captchasettings.showonblogcommentpage False
captchasettings.showonnewscommentpage False
captchasettings.showonproductreviewpage False
captchasettings.showonapplyvendorpage False
Now i have to figure out how to make captcha work