I'm not sure what you're talking about. There is no setting to enable or disable image resizing. The only thing that would have any influence over image sizing would be the HTML that is used to show the image, but I'd have to see it to know what's happening.
Please remember to always post a link to your site when having issues with something on the front-end; I can't even begin to diagnose the cause of a problem if I can't see what's happening and inspect the code with
Firebug.