By now all of us at one time or another have had to read a construed image and type the letters and numbers we saw into a textbox.  This test is what is known as a CAPTCHA, and it prevents bots (programs created to spam websites among other objectives) from submitting a form on a website.  The reason it prevents bots from submitting a form (and its agenda) is because bots can't decipher the text within an image, and thus it cannot fill out the correct response in the textbox.  Alt... Read more.