That thing is called a CAPTCHA.

like this CAPTCHA. (Text invisible toaster)

Code

All of you have probably filled out a captcha.

Country Code

PIN Code

Code Folding

Country code

Zip Code

Postal Code

Postal code

bkisofs code

Postal code

Postal Code

Character code

Code unspecified.

A code.

Code 09.

Code Red!

Code breaking.

Code six

Vehicle code?

Code 431.

Morse code?

Code red.

Secret Code

Binary code.

Code yellow!

The code.

The Code.

Code black.

You might not have known it was called a challenge captcha.

Code Blocks IDE

Gift card code

Code Poets Dream