Serve retina display images in Stack Exchange content?

After a recent hardware upgrade, I've run into the problem of not being able to easily use the screenshots I take for Stack Exchange questions and answers anymore because they are massive.

If I had an image editor installed I could resize the images rather quickly. A Photoshop droplet would be one easy solution. And there are others. But I haven't installed any image editing software yet, nor have I found any of the other solutions suitible.

I wonder though, if maybe the answer doesn't lie in crushing the content down again, but rather in letting it live in its original retina glory.

Is there some kind of syntax I can put around my images to tell Stack Exchange "this is a retina res image", so that it will be served at full-res to retina visitors and at half-res to non-retina visitors?

Thanks.