I'm looking for Javascript code for letting the user draw a line (on an image).

Just as the line tool in Photoshop (for example):

The user clicks on the image, drags the mouse (while the line between the start point and the mouse point is dynamically drawn on mouse drag).

I would also need a callable function to send the page the start and end coordinates.

I've found this very nice script for area selection:
http://www.defusion.org.uk/code/javascript-image-cropper-ui-using-prototype-scriptaculous/

and I've found many script for drawing lines (and other shapes in JS), but could not find what I'm looking for.

Thanks