You can create a css class and use it with your image. Here is the css:
.roundedcorners
{
-webkit-border-radius: 10px;
-khtml-border-radius: 10px;
-moz-border-radius: 10px;
border-radius: 10px;
}
Apply this css to your image as:
<img src="yourimagesource" class="roundedcorners" />
But this approach does not work with IE