Selecting multiple images
Your code is actually very good. 

I'd advice against using OOP there. It's an overused tool which, when not necessary, only makes things more complex. JavaScript works very well without it. I'd recommend a more functional style. So, if you want to make your code more reusable, you could abstract your functions to work with any kind of collection. You could also use existing functions to define others:

function removeFirst(array,obj) {
    array.splice(array.indexOf(obj), 1);
};
function without(array,obj){
    return array.filter(function(element){
        return element !== obj;
    });
};
function count(array,obj){
    return array.length - without(array,obj).length;
};


Then, counting an image would be, for example:

count(images,my_image);


But before I'd suggest checking some functional JavaScript libraries such as underscore.js, which already implement similar functions in very clever manners. Using them in your daily code will make it smaller, simpler, more readable and robust.