.avatar-image-container {
background:url(http://farm3.static.flickr.com/2493/3936605180_5f80a4d847_o.gif); width:35px;
height:35px;
}
.avatar-image-container img { border:none;}

<dl id='comments-block'>

<dl expr:class='data:post.avatarIndentClass' id='comments-block'>

<a expr:name='data:comment.anchorName'/>

<b:if cond='data:comment.favicon'>
<img expr:src='data:comment.favicon' height='16px' style='margin-bottom:-2px;' width='16px'/>
</b:if>
<a expr:name='data:comment.anchorName'/>
<b:if cond='data:blog.enabledCommentProfileImages'>
<div expr:class='data:comment.avatarContainerClass'>
<data:comment.authorAvatarImage/>
</div>
</b:if>