Serving images from an alternate host

I'm in the business of marketing product from other companies, those companies submit their product to me and I market it through my site. Along with the product comes images and we are talking millions of them that change daily.

I started heading down the path of proxying my partner sites image urls rather than downloading, processing and storing every images on my end. Although this works, it doubles the bandwidth for me, so I'm looking for a better approach.

One of the main issues I face is my site is https and some of my partner sites are not which results in a certificate error if I attempt to host them directly.

I happened to see an example where someone was doing something like this.

http://ift.tt/1DdVApM

So I did some research on it and didn't turn up much of anything on it.

So my question, is this a valid way of doing it, or is it just someones way of setting up their proxy? If it is a valid way, would this address my bandwidth / ssl concerns?