Converting img src data to octet-stream

Question

I am working on a REST call that has a body that accepts a application/octet-stream.

I need to use this API to send an image that from a "src" atributte from an HTML element:

<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAQAA ... AAAAAElFTkSuQmCC">

How can i convert this type of data to send trough this API?

API:

$.ajax({
        url: url,
        async: false,
        contentType: 'application/octet-stream',
        method: 'POST',
        data: imgData,
        processData: false,
        success: function(data) {
                //Do something
        }
        error: function(x, e, s) {
                //Do something
        }
});

I tried to use the function provided in here. It completes the call, but the file on the other part is not saved as a image file.