rex = re.compile(r'(href=(\"|\'|\.\.)([^>]*?)(\"|\'|(class=))(.*?)><img)', re.S)
        urls = [c[2] for c in rex.findall(s)]

        <tr>
            <td valign="top" class="class">
            <a href="http://www.domain.com/url1" target="_new" rel="nofollow"><img style="border: 1px solid #000000;" name="name" id="id" src="http://domain.com/1.jpg" width="400" height="500" /></a>
            </td>
            <td valign="top" class="class">
            <span class="title">title</span><br>
            text<span class="new">text</span> <br>
            <br>
            <a href="http://www.domain.com/url2" class="class"  title="title">title</a>, <a href="http://www.domain.com/url3" class="class"  title="title">title</a>  <br><br>
            </td>

r"""href=["'](.*?)["'].*?<img"""

import lxml.html
 
doc = lxml.html.fromstring(html)
print doc.xpath('//img/parent::a/@href')  #['http://www.domain.com/url1']

html = """<tr>
<td valign="top" class="class">
<a href="http://www.domain.com/url1" target="_new" rel="nofollow"><img style="border: 1px solid #000000;" name="name" id="id" src="http://domain.com/1.jpg" width="400" height="500" /></a>
<a href="http://www.domain1.com/bad_url1" target="_new" rel="nofollow"><img style="border: 1px solid #000000;" name="name" id="id" src="http://domain.com/1.jpg" width="400" height="500" /></a>
<a href="/url2" target="_new" rel="nofollow"><img style="border: 1px solid #000000;" name="name" id="id" src="http://domain.com/1.jpg" width="400" height="500" /></a>
<a href="/bad_url_stopword" target="_new" rel="nofollow"><img style="border: 1px solid #000000;" name="name" id="id" src="http://domain.com/1.jpg" width="400" height="500" /></a>
</td>
<td valign="top" class="class">
<span class="title">title</span><br>
text<span class="new">text</span> <br>
<br>
<a href="http://www.domain.com/url2" class="class"  title="title">title</a>, <a href="http://www.domain.com/url3" class="class"  title="title">title</a>  <br><br>
</td>"""
import lxml.html
 
doc = lxml.html.fromstring(html)
print doc.xpath('//img/parent::a[not(contains(@href, "stopword")) and starts-with(@href, "/") or starts-with(@href, "http://www.domain.com") ]/@href')

print doc.xpath('//img/parent::a[not(re:match(@href, "(first|second|third)"))'
                ' and starts-with(@href, "/")'
                ' or starts-with(@href, "http://www.domain.com")]/@href',
                namespaces={"re": "http://exslt.org/regular-expressions"})

         <a href="/url/url.html">
	<span class="image"><img src="http://host_ip/img.jpg" alt="text"></span>
	<span class="text">text</span>
	<span class="class1">class1</span>
	<span class="class2">class2</span>
</a>

'//img/parent::a' на '//a[descendant::img]'

<li>
<a href="/url/url1.html" />
<img src="http://ip_address/1.jpg" width="100" height="100" border=0 alt="title" /></a>
<h3>title</h3>
<div class="class"><i>class:</i> <a href="/url2/">url2</a>, <a href="url3">url3</a>, <a href="url4">url4</a>, <a href="url5">url5</a></div>
</li>