The simplest way to do it without adding an extra overlay element, or using two images, is to use the :before or :after selector.
.image {
position: relative;
}
.image:hover:after {
content: "";
position: absolute;
width: 100%;
height: 100%;
background: rgba(0,0,0,0.1);
top: 0;
left:0;
}
This will not work in older browsers of course; just say it degrades gracefully!