Image with cookie script

[GilbertLiddell]

Hi,

I have three sites (domain1, domain2 and domain3).
Currently, a user clicks a button on domain1 to start their journey, they are then sent to domain2. On domain2 the user clicks a button to complete their journey.

This is what I want to do, when the user clicks the button on domain1 to start their journey, a cookie is saved from domain3 and when the user clicks the button on domain2 to complete their journey the cookie on domain3 is updated.

I know cross domain cookies are an issue however i've heard of people using the image <img> to get round this problem by placing a hidden image on the pages where the button is and setting is src in script.

Any ideas??