.readmore-fd {
width: 101px;
height: 24px;
display: block;
font-size: 10px;
text-decoration: none;
background-repeat:no-repeat;
background-image:url(link ảnh 1);
}
.readmore-fd:hover {
background-image:url(link ảnh 2);
}

<div class='post-body entry-content'>
<data:post.body/>
<span class='rmlink'><a expr:href='data:post.url'>Read More...</a></span>
<div style='clear: both;'/> <!-- clear for photos floats -->
</div>

<a class='readmore-fd' expr:href='data:post.url'/>

<div class='post-body entry-content'>
<data:post.body/>
<span class='rmlink'><a class='readmore-fd' expr:href='data:post.url'/></span>
<div style='clear: both;'/> <!-- clear for photos floats -->
</div>