<img data-alt-src="https://minecraft.net/static/theme/img/gif/menu-realms.gif" src="https://minecraft.net/static/theme/img/gif/menu-realms--reversed.gif" />



var sourceSwap = function () {
    var $this = $(this);
    var newSource = $this.data('alt-src');
    $this.data('alt-src', $this.attr('src'));
    $this.attr('src', newSource);
}

$(function() {
    $('img[data-alt-src]').each(function() {
        new Image().src = $(this).data('alt-src');
    }).hover(sourceSwap, sourceSwap);
});

<img data-alt-src="https://minecraft.net/static/theme/img/gif/menu-realms.gif" src="https://minecraft.net/static/theme/img/gif/menu-realms--reversed.gif" />

<br><br>

<img data-alt-src="https://minecraft.net/static/theme/img/gif/menu-realms.gif" src="https://minecraft.net/static/theme/img/gif/menu-realms--reversed.gif" />

<a class="js-master-header-quick-options menu-link" data-mouse-over-icon="https://minecraft.net/static/theme/img/gif/menu-realms.gif" data-mouse-out-icon="https://minecraft.net/static/theme/img/gif/menu-realms--reversed.gif" href="#">
 <span data-mouse-over-target="" class="icon-menu icon-menu-realms" style="background-image: url(https://minecraft.net/static/theme/img/gif/menu-realms--reversed.gif);"></span>
 <span class="menu-link__label">Realms</span>
</a>

<a data-over="...gif"  data-out="...gif">
   <span style="background-image: url(EntraAquiAsImags);"></span>
   <span>Home</span>
</a>