I have a banner with 1000px of width and 250px of height.
<a href="#">
<img width="1000" height="250" border="0" src="http://oboshto.ru/upme/shits/banner1000.jpg" alt="">
</a>
your border is there, the reason it's not on the right and bottom is your container has width:998px; height:248px;
but your image has width="1000" height="250"
either add two more pixels to your container so that the image isn't breaking out or set the container to overflow:hidden;