Ah ok, now I understand what you mean.
SMF, as far as I know, doesn't have anything like this (and it wouldn't be a bad idea actually), apart from the mod you linked.
Unfortunately it has not been updated for version 2.1
Has this been split off and you're referring to a different topic?
I would like to understand how to resize the images that a user uploads to save MB
Only way is with a mod
https://custom.simplemachines.org/index.php?mod=4087
Because this basic option is not in smf core.
With this application, a 7MB photo became 159.66KB
This isn't a 'basic' option, this is surprisingly complicated to get right and it needs to be optional because photography forums and art forums will want the images not resized or compressed. And for some of the images I've had uploaded in the past, it was actually impossible to resize the image on the server.
But there is a mod as mentioned that can do this for many images.
99% of forums are not about art or photos.
More than 80% of forum traffic comes from mobile phones.
The admin must decide whether or not to activate the resizing as happens for all cims (wordpress, joomla, magento, prestashop etc. but also xenforo, vbulletin or ipb).
The photo I resized with that plugin is 44 times smaller.
Today users upload a lot of photos with their mobile phone and the site admin can't have hundreds of GB of space occupied by large photos if he doesn't need it.
So, use that mod. I know I do