Captcha in mobile application and web application

I have read some web si开发者_开发问答te that captcha is not needed in mobile application.

I have some doubts.

Why captcha is needed in a web application and not needed in a mobile that access the same application?

First off, it is relatively simple to create a bot to crawl the web (including web applications) and submit forms. This is where a classic CAPTCHA solution comes in.

It is comparatively harder to automate data submission within native apps. This is due to the fact that you cannot just write an automated script to discover <form> elements within the source code and then mimic form submission. Also, you'll need to (purchase and) install the application (on a physical device or in a simulator).

As a side note: web applications for mobile devices can do a lot to make the CAPTCHA process simpler. Different versions of slider CAPTCHA's come to mind.