Fill-in web forms are under attack of web hackers. They write robots (programs) that look for forms and then try to fill them in automatically in the hope to get a response that contains e-mails to which they can then send spam.
To make it impossible or very difficult for robots to fill in our form, we test for graphic character recognition which is easy for humans but difficult for spam programs. The ten digits you see in the 5×5 grid are in fact images, therefore analysing the page code by program will reveal the names of the images but not the digit that is painted on them. To recognise them and click them in the right sequence the image has to be converted to the digit, which is easy for humans. Robots can not yet do that, so they cannot successfully submit the form.
Thank you for understanding that we need this protection and for taking the trouble to click the images.
Your GAC-EPA website administrator.