Thanks for the reply.
That is the way I do it at the moment but it is inefficient as some less technical clients do not want to start opening PhotoShop or Paint and trying to figure out how to draw on an image. They all know how to use a forum though and to simply draw on an image to point something out as their reply
is fast, logged and requires no external software.
There are many "artwork approval" orientated websites appearing on the net but they ask for monthly subscription fees of $40 a month up. They have more detail to them like version control and comment tracking but that is overkill for the simpler version that I suggested here.
Something like this: http://ianli.github.io/raphael-sketchpad/
but the canvas has my image in it.