How to auto resize image?

[eluser]Kency[/eluser]
Hello everyone

Im new with Codeigniter, i have a question is: how to auto resize image?

because i use CKEditor to add image into my content, and then show it on view.

But its size very large, and i try many times to search on google but i got nothing.

i want when image post by CKEditor if it large more than 400x200 it will auto resize

How can i do that?