From a thread with Pavel:
"And images will be retrieved from the media library or local file system, which will provide great flexibility. Some often used images, like boxes and arrows, might be bundled with the product. Annotations will have fade-in, fade-out time settings."
See also: http://dev.tiki.org/Video+annotations
Related: https://sourceforge.net/p/jcapture-applet/tickets/24/
https://code.google.com/p/svg-edit/issues/detail?id=985