You may enable or disable this by going to "My Account" --> "Global Preferences" --> scroll down to the bottom of the page and check or uncheck "Automatically scale down large images for faster download and cleaner presentation".
Please be aware that there are currently a couple of work flows where there is a problem with this option (however, it is not a problem for most customers). Our engineers are working on correcting those problems. If you are having trouble with your enlarged images, please let us know in detail exactly what is happening so that we can take a look.
