CORS header not set - can I request an image url and then serve it back to myself?

I am attempting to populate a WebGL Earth with meshes that are compiled from images. These images are cross-domain, and hosted on a server where setting the appropriate headers isn't an option. Can I XMLHttpRequest the image urls, and then serve them back to myself via PHP to bypass CORS errors?

Or, more specifically, can I use my own webserver as a proxy to serve img urls back to myself (to get around CORS) in a WebGL context?

EDIT: The real question here is if I can use my own webserver as a proxy to pass the urls, or if I'll have to actually download each image to the server to then use it.