Web forms
Forms can be combined with various scripting languages to allow developers to create dynamic web sites. This includes both client-side and/or server-side languages.
The de facto standard client-side scripting language for web sites is JavaScript. Server-side programs can do a vast assortment of tasks to create dynamic web sites тАФ from authenticating a login through to retrieving and storing data in a database to spell checking to sending e-mail тАФ quite unlike client-side programs. The advantage of server-side over client-side is the concentration of functionality onto one computer (the server) instead of relying on each web browser implementing all of the various functions the same.
PHP is one very common language used for server-side languages and is one of the few languages created specifically for server-side programs.
A PHP script may
- Display the information on another page (ex: asking for a user's name and then displaying it on the web page)
- Act as a logon interface
- Post the data to a database (ex: mySQL, an ASCII file, etc.)
- Store the information on the viewer's computer in an HTTP cookie
- Generate an e-mail, either using the data or including said data in the e-mail's contents (possibly as an e-mail attachment)
CAPTCHA
A CAPTCHA is a type of challenge-response test used in computing to ensure that the response is not generated by a computer. The term "CAPTCHA" is a contrived acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart."
CAPTCHAs can be deployed to protect systems vulnerable to e-mail spam. CAPTCHAs have also found active use in stopping automated posting to blogs, forums and wikis. CAPTCHAs also serve an important function in rate limiting, as automated usage of a service might be desirable until such usage is done in excess, and to the detriment of human users. In such a case, a CAPTCHA can enforce automated usage policies as set by the administrator when certain usage metrics exceed a given threshold.
A modern CAPTCHA, rather than attempting to create a distorted background and high levels of warping on the text, might focus on making segmentation difficult by adding an angled line.