Steps

1. Shutdown your JIRA application.

2. Execute the following SQL to identify the record to update:

   SELECT s.* 
   FROM   propertyentry e 
          JOIN propertystring s 
            ON e.id = s.id 
   WHERE  property_key = 'jira.maximum.authentication.attempts.allowed'; 

3. And run the following SQL to set that record to an empty string, which is the equivalent of unlimited authentication attempts, bypassing CAPTCHA validation:

   UPDATE propertystring 
   SET    propertyvalue = '' 
   WHERE  id = <id from step 2>;

4. Start JIRA application.

 Currently, CAPTCHA can not be disabled on Oracle databases. There is an open JAC ticket that can be voted on and watched for more information:

JRA-41240 - Getting issue details... STATUS