Pixle location of Image when Clicked

[onlyican]

hahahaha, this is gonna be fun I think

Going to
http://onlyican.com/images.php
You will see an image
and if you play with the form at the bottom, u see that depending what you select, it makes a box turn black

This is using GD LIB
The orig image (green with the yellow stripes) is one image
THe black box is another image

What I am looking for, is if someone clicks on that image, for me to find out the image pixle location of where they clicked

I dont want the geographical location of the click (where 0,0 is the top left of the screen)
I need it to be the image location
(where 0,0 is the top left corner of the image)

I think this is client side scripts (Javascript), as I dont think it can be done in server side scripting(php)

By the way, You may have guessed. I am using php

[AndyB]

If you use the image itself as a submit 'button', then php will pass the x and y co-ordinates (relative to the upper left corner of the image) of where it was clicked as the 'name' values of the submit button, i.e. $_POST['submit_x'] and $_POST['submit_y']

[onlyican]

Now I never knew that

Thanks