I have the following iframe:
It's written in the limitations section of the doc: http://html2canvas.hertzen.com/documentation.html#limitations.
The script doesn't render plugin content such as Flash or Java applets. It doesn't render iframe content either.
Screen capture using JS raises security problems.
Recently I've been trying carota (https://github.com/danielearwicker/carota) with some success to render HTML text on a canvas. However, it only handles a small subset of HTML.
There is also the SVG foreignobject
approach which makes it possible to render DOM objects in a canvas: https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Drawing_DOM_objects_into_a_canvas
Unfortunately, it is not implemented in IE, including IE 11.