[css] How to make image hover in css?

You're setting the background of the image to another image. Which is fine, but the foreground (SRC attribute of the IMG) still overlays everything else.

.nkhome{
    margin-left:260px;
    top:170px;
    position:absolute;
}
.nkhome a {
    background:url(Images/btnhome.png);
    display:block; /* Necessary, since A is not a block element */
    width:59px;
    height:59px;
}
.nkhome a:hover {
    background:url(Images/btnhomeh.png);
}


<div class="nkhome">
    <a href="Home.html"></a>
</div>