Overlaying Lines on an image

MY QUESTION IS... is there an easy way to draw lines from point A,B,C
and D. The lines do not need to do anything but appear on the screen.

That'd be some javascript then.

I am trying to make it so the user can see there path as they click
their way through the image.

I'd go with rmagick. The lines could be added to the image server
side so they will look the same everywhere.