Image sizes

I want all pages to have the option to have the "1040x585" size option as excerpt has for blog entries. I've tried adding a custom photo size in functions.php but it doesnt show up as an option. Now on all pages and posts when I try to add a photo there is no option to pic a cropped 1040x585 version so the photos ends up being huge. How do I make this an option for all pages so we don't have to manually edit all photos before uploading. Thanks in advance!