Image above another as a stamp using css

I have an image on the screen where I want to add a stamp, the problem is that as this image is inside a foreach, so if I take the id of the image, it will be repeated.

<div class="panel-body">
    <div class="carimbo-foto">
        <img src=~/Content/imagens/carimbo.jpg class="img-responsive" id="carimbo" alt="" width="128" height="128">
        <img src=~/Content/imagembanner/@item.LOCALIMAGEM class="img-responsive" id="banner" [email protected] width="560" height="315">
    </div>
</div>

CSS:

#carimbo-foto{
   position:absolute;
   z-index:0
}


#carimbo {
    position: absolute;
    left: 50%;
    top: 50%;
    margin-left:-64px;
    margin-top:-73px;  
    z-index:1
}

Result: