Immediately self executing function and “this”

I want to create a javascript library, so I thought making it an immediately self executing function would be a nice thing to do to ensure scope safety and everything.

But now I'm running into a problem with using the "this" keyword that I don't quite understand.

How can I make a code like this work correctly? Currently, it tells me that "image" is undefined.

(function() {

    function lib() {
        this.image = document.getElementById("image");
        this.parts = [
            {name: "part1", num: "1"}
        ];

        this.init = function() {
            $(parts).each(function() {
                var partNum = this.num;
                image.getElementById(partNum).addEventListener("click", function() {
                    toggleHighlight(partNum);
                }, true);
            });
        };
    }

    window.lib = new lib();
})();

window.lib.init();

How can I access the image property?