<div class="gradient-box">
<img src="your-image-here.jpg">
</div>
html = '<img class="gradient" src="your-gradient-here.png">';
$('.gradient-box').append(html);
.gradient-box {position: relative;}
.gradient-box img { height: 100px; width: 100px; position: absolute; left: 0; top:0; z-index: 1;}
.gradient {z-index: 3;}