Should creating email accounts have an API? How would the captcha be presented? How about adding reviews of products?
The point of an API is to have a clear interface so that programs can be built on a service, and captchas exist to try to block bots from using services.
do:
server->return any errors
client->display errors
client->ask user for account name
client->server->request account name x
while ( server->x is invalid account name )
<< Repeat above loop for password >>
do:
server->return new captcha
client->display captcha
client->take user input
client->server->send captcha text
while(server->captcha does not match)
server->return success message