[peterska2]

<if condition="$post[field11]"><img src="images/$post[field11].gif" alt="$post[field11]"></if>
<if condition="$post[field10] && $post[field9]"><img src="images/$post[field10]_$post[field9].gif" alt="$post[field10] $post[field9]"></if>
<if condition="$post[field12]"><img src="images/$post[field12].gif" alt="$post[field12]"></if>

That should work for you.