views 2 - how to fetch filepath of image field for output rewriting
One trick I like to use is adding a field that contains the value I need, then hiding it from display but using it's token value for your original field's override.

So your view fields would look something like:

image path (hidden from display)
image (using value from the above field)


Keep in mind that the order is important here, so you only have access to tokens that are above the field you want to use them in.

You may need to tweak the settings of the path field to make it the style of url you need (relative, absolute, etc).