Или как-то так
<style>
.container {
position:relative;
display: inline-block;
}
.mask {
position:absolute;
top: 0px;
left: 0px;
width:100%;
height:100%;
background-image: -webkit-radial-gradient(50% 50%, ellipse closest-side, rgba(255,255,255,0) 40%, rgba(255,255,255,1));
background-image: -moz-radial-gradient(50% 50%, ellipse closest-side, rgba(255,255,255,0) 40%, rgba(255,255,255,1));
background-image: -o-radial-gradient(50% 50%, ellipse closest-side, rgba(255,255,255,0) 40%, rgba(255,255,255,1));
background-image: -ms-radial-gradient(50% 50%, ellipse closest-side, rgba(255,255,255,0) 40%, rgba(255,255,255,1));
z-index: 100;
}
</style>
<div class="container">
<image src= "http://www.imageup.ru/img133/2542020/preload.png"/>
<div class="mask">
</div>
</div>