I haven't got the option to choose within the content block elements for 'Single Image' (visual composer). I contact them and they said I need to contact the theme author. Could you help? See message below from visual Composer:
The element is most likely removed by the theme author using: https://wpbakery.atlassian.net/wiki/pages/viewpage.action?pageId=524329
You can get in touch with him and get rid of the above code to get it back. Kindly check.