How can I reduce the file sizes of the original versions of uploaded image files? I have a Drupal 7 site that allows users to upload pictures of themselves.  While the pictures aren't using much space on the server's filesystem now, I am worried that if my membership grows substantially I will have to add more space to cover all the images.

Right now, I allow users to upload images up to 10 MB in size.  I want to leave this limit high if possible because many of my users are not technically skilled and they do not know how to resize their images.

At the same time, the largest resolution that will be used on the site is 1024x1024.  So, I have configured the core image field to automatically scale down the images to 1024x1024.  This significantly reduces the file size.

Are there any other ways to automatically reduce the size of uploaded images?  Please note that I am talking about the original files, not image styles.
Interesting question - this should be a standard option on community distributions to avoid the space issue you raised but you're right that the focus seems to be on image styles as a solution..

Two ways to handle this


More custom way would be to add a hook_form_alter to your form that would add a submit handler to resize the image file after uploaded to the correct size -- if you are able to do image styles than your server already has the image libraries needed to do this.
An easier way would be to use an uploader that can be configured to do this work for you on the upload. One example is the plupload module / widget which has a clientside resize option during the upload (also saving bandwidth)


resize

Enables plupload to resize the images to clientside to the 
specified width, height and quality. Set this to an object with those
parameters.