I´ve modified the code to be able to submit custom images. I simply uncommented your code and patched the line 30 on cck_map.js:

//i.image = 'http://'+this.tld+'/'+img;
i.image = img;

It also could be easy to add a new functionality to give the posibility to the users to simply upload new markers to the icon directory and then be catched by the module. In this line:

$icon_files = array("house.png" => "house","hotel.png" => "hotel", "picnic.png" => "picnic", "airport.png" => "airport");

changing the array by the function looking at the directory should be easy. I´d like to help so if you like my idea i´d love to patch the file on the cvs.