I tried setting some math characters (e.g 'μ') in a title of a figure, like so:

    var figure = {
      layout: {
        title: 'Normal (μ = 0, σ = 1.0)',
      }
    };

However, when I call plotly.getImage(figure, ...) a error is returned and it looks like the server returned a "500 Internal Server Error".

When I use the graph builder on the plot.ly site, I see that Chrome POSTs JSON in the form title: 'Normal (\u03bc = 0, \u03c3 = 1.0)', however Node.js seems to send it literally title: 'Normal (μ = 0, σ = 1.0)'. Reading the JSON spec, how Node.js is sending it is valid, however, hacking the plotly/index.js, and changing the output of JSON.stringify to use \u0XXX notation seems to work.

So please either change your Node.js API to encode in a way that is suitable, or please change your server to accept all valid JSON.