This is an example of a customized captcha incorporated into a dropdown that has an encrypted hint.
Many sites are visited by robot crawlers looking for forms that can be used to email spam or populate databases with spam. This is an example of how I protect an online form from these nefarious deeds. By using encryption in my code, I can hide the hint from robots, however, a human can read it.
The customized captcha is hidden in the form and looks like an ordinary dropdown box with days of the week as options. This dropdown box is required and a day of the week must be selected or the form cannot be submitted. Every day the answer changes and there is a hint below the box that changes depending on the appropriate day.