There are several ways to solve your problem, even all derived from a single one. You can use ready made solutions - by searching Google, you will find several free and/or paid libraries - or create them from scratch.
Here I propose an example so you can work on it. It just magnifies/reduces the image without great beauty involved.
var entidade = document.getElementById('imagem');
// Altere o número para a apliação/redução desejada
var fator_lupa = 2;
entidade.onmouseover = function () { this.style.width = (this.clientWidth * fator_lupa) + "px"; };
entidade.onmouseout = function () { this.style.width = (this.clientWidth / fator_lupa) + "px"; };
<img id="imagem" width="200" src="https://www.google.com/images/srpr/logo11w.png" />
Here is a link from Jsfiddle for example of the code in operation in case the Sopt preview does not work: Jsfiddle
I hope I’ve helped!
There are some cool jQuery plugins to do these things. One of the most interesting I’ve seen is the jQuery Zoom. Besides beautiful and functional your "installation" is very easy, have the step-by-step right there on the site. If you have problems let me know.
– Dirty Old Man