Something

        if (servletContext == null) {
            servletContext = (ServletContext) extContext.getContext();
        }
        if (Util.isPrefixMapped(Util.getFacesMapping(context))) {
            // if an image has been requested of the ViewHandler,
            // set responseComplete() to terminate the remainder of
            // the lifecycle and return null;
            String viewId = viewToRender.getViewId();
            String mimeType = servletContext.getMimeType(viewId);
            if (mimeType != null && mimeType.startsWith("image")) {
                context.responseComplete();
                extContext.dispatch(viewId);
                return;
            }
        }