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How does it work? I'm in the same boat as jsdalton -- I thought it was't possible.

The person sending the emails creates a dynamic web page. It can use all of the latest and greatest web technologies. (AJAX, WebSockets, CSS3, SVG, etc) Then they create a Web Crop in our dashboard, and we give them an HTML embed code.

When a user opens the email, it points to an image on our servers. At that point, we load the dynamic web page, take a screenshot, crop it, and render it in your browser. But at that point instead of closing the connection, we leave it open. Every second, we repeat the process, replacing the old image with the new one.

Crafty! How do you get the image to overwrite? I would think that you could only append to the image data that's already been transmitted.

Our current method uses the content-type multipart/x-mixed-replace. (Remember http://www.wired.com/wired/archive/5.03/ff_push.html? Good times...) When the request starts you specify a boundary string; then every time the browser sees that boundary string it knows to replace the existing image.

it's (very) cool, but x-mixed-replace is not supported in all browsers. I sure hope the browsers that support it don't end up dropping their support.

That's cool, thanks for the explanation.

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