CMS question

Lets say somebody wants a website with clothing and he wants images for all his clothing items, but he wants to update his site hisself with a CMS system.
Lets say the clients knows nothing about computers and images/photoshop or whatever.
Its very simple to make him a CMS system that makes him able to type in a text for the item lets him upload a picture from his harddrive and he can give it a price.

If the guy takes a good quality picture with a digital camera the picture will be 2 mb.
I can let the CMS system scale the images to the correct size but if the size of his original picture that he is going to upload isn’t proportional scaleable to the sizes of the CMS then the image will stretch. And one other problem if the client uploads a 2 mb images and lets the CMS scale it then still the image will be 2 mb to load.
Is there a CMS system that can sort of save a image for web and cut of parts so it can scale proportional so the client can really update everything hissefl.

Any info is welcome.
Thanks in advance