Node Express sending image files as API response

I Googled this but couldn't find an answer but it must be a common problem. This is the same question as Node request (read image stream - pipe back to response), which is unanswered.

How do I send an image file as an Express .send() response? I need to map RESTful urls to images - but how do I send the binary file with the right headers? E.g.,

<img src='/report/378334e22/e33423222' />

Calls...

app.get('/report/:chart_id/:user_id', function (req, res) {
     //authenticate user_id, get chart_id obfuscated url
     //send image binary with correct headers
});

There is an api in Express.

res.sendFile

app.get('/report/:chart_id/:user_id', function (req, res) {
    // res.sendFile(filepath);
});

http://expressjs.com/api.html#res.sendfile