How to auto resize image?

[eluser]Kency[/eluser]
@weboap thank for your reply but i dont mean that

i mean i use CKEditor to link image and display it with [IMG] tag (CKeditor do it for me)

it like when you post image on forum you have editor and you click on img tag to embed it into your post

and my situation like that, i want all my pictures post by CKeditor will be auto resize like a mod in VBBulletin Forum