Anti-bot protection in the form of graphic captchas is going for good. It has been several years already, the captchas are recognized by various services and various application (free/non-free).
The captchas on the site can be customized continuously but this is dead end road. The captchas can push off the visitor of the site (who can be your potential customer). This type of anti-bot protection is outdated, and will go for good in 2-3 year with introduction of more modern user authentication systems.
The state of art are provided with secure protection against Spam-bots with use of the following techniques:
It takes not more than 20-30 minutes (one day for the non-expert) to ensure site protection against robots without using such repulsive for users technologies as captchas.