Ah, non vi preoccupate, ho risolto:

Codice PHP:
checkbox: function(targetcallback)
    {
        var 
image target.find("img");
                
                
// Creo un puntatore all'oggetto
        
var self this;

        
checkbox target.find(":input");
        
target.click( function(e)
        {        
            if (
self.state true){
                
image.attr('src''/images/CheckFalse.png').css({top"-0.75em"left"0.75em"});

                                
// e poi lo uso per modificare this.state anche se sono fuori dallo scope del "this" dell'oggetto
                
self.state false;
                if (
checkbox.length){
                    
checkbox.attr('checked'false);
                }
                if (
callback){
                    
callback(false);
                }
            }
            else {
                
alert("trigger");
                
image.attr('src''/images/CheckTrue.png').css({left"1em"top"-0.15em"});
                
self.state true;
                if (
checkbox.length){
                    
checkbox.attr('checked'true);
                }
                if (
callback){
                    
callback(true);
                }
            }
            
e.stopPropagation();
            
e.preventDefault();
            return 
false;
        });
        
        return 
this;
    },