Creates a simple math test a visitor must solve when submitting a form
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This class is used to create an image to be included in an online form that shows a simple math test the visitor must solve when submitting the form. The operands and operation are stored in the $_SESSION data for the page. After submitting the form, the visitor's answer is checked by calling the verify() method to compare their entry vs. the session data. If an error is found, the form submission should be rejected.


Limitations and Scope

One problem with this sort of form protection is that the math problems need to be very simple for average users to succeed. Answers are limited to integers in the 0-99 range so that users can calculate them. Even without using optical character recognition to parse the image and calculate the correct answer, a bot attempting numerous trials will succeed with a small but harmful percentage once it knows the field requires numeric input and the valid range. This is a start but the challenge is to make it harder for bots to defeat while keeping it easy enough for humans of almost all capabilities to succeed.

Used in isolation, this test is far from adequate protection on a form where anything more than minimal security is needed because of the statistically high possibility of getting a correct answer from a random selection.

This class, as written, is intended to reduce noise submissions on a survey form, not to preventing someone from biasing the outcome.

Released Versions

  •, 27 September 2018, added Limitations and Scope section
  • 0.9, 23 September 2018

Code Style


This project is licensed under the BSD-3-clause license


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