Changing [img] variable
 

When images are displayed by default they go to the left but i want them to be centered by default, i tried inserting a replacment variable. It work sort of but only centered if you hit edit and save then the [center] tags were placed and it centered. This what i tried to use

search for: [img replace with:
Objective is once they hit submit a post that it will automatically center the image or as soon as the image url is put in the box and click ok it puts the [center] tags in automatically.