the input image. If missing, a transparent 800x600 png is used.
resultId
the id of the div in the UI where the annotation (the drawn polygon) is stored.
Only relevant when the widget is used in shiny. Defaults to "annot_id".
brushWidth
default to 3 pixels.
brushColor
Any valid CSS color. For example "red", "rgba(255,93,0,1)", or "#1c4564".