I've modified an existing plugin and added the ability to DYNAMICALLY auto resize user avatars. It does it PROPORTIONATELY so that the image doesnt get stretched. You simply type in the maximum height/width and it will resize the image (without touching or editing the original file) to fit within that restriction.
https://vborg.vbsupport.ru/showthread.php?p=952624
This could also be used for profile images and all image attachments, you simply go in and use the imageresize.php code where you want to restrict the file dimentions on any image.