Subdomain image hosting

Hello,

I am having difficulty uploading images onto a subdomain. However, if the images are already on the subdomain, and I include their absolute url into a post, they show up, no problem.

In the Settings->Miscellaneous, I have included the Full URL Path to Files http://images.[mysite].com/images (777 for now), and, although there is no error saving the attachment, the image is not uploaded. The Media Library contains information about the image, including the url (that would work in a browser if the image was in that folder), but not the image itself. And ssh-ing over to the appropriate folder shows that nothing has been uploaded.

Any ideas as to what may be the issue? I appreciate any and all assistance!