Código PHP:
preg_match("/<img width\=\".*\" height\=\".*\" src\=('|\")(.*)('|\") .*( |)\/>/U", $the_content, $matches);
Código PHP:
<div id='gallery-1' class='gallery galleryid-4694'><dl class='gallery-item'>
<dt class='gallery-icon'>
<a href='http://movilzone.org/software/pocket-player/attachment/3_p2-2/?preview=1&template=tma&stylesheet=tma' title='3_p2'><img width="150" height="150" src="http://movilzone.org/wp-content/uploads/2009/06/3_p2-150x150.jpg" class="attachment-thumbnail" alt="" title="3_p2" /></a>
</dt></dl><dl class='gallery-item'>
<dt class='gallery-icon'>
<a href='http://movilzone.org/software/pocket-player/attachment/3_p3-2/?preview=1&template=tma&stylesheet=tma' title='3_p3'><img width="150" height="150" src="http://movilzone.org/wp-content/uploads/2009/06/3_p3-150x150.jpg" class="attachment-thumbnail" alt="" title="3_p3" /></a>
</dt></dl><dl class='gallery-item'>
<dt class='gallery-icon'>
<a href='http://movilzone.org/software/pocket-player/attachment/3_p1-2/?preview=1&template=tma&stylesheet=tma' title='3_p1'><img width="150" height="150" src="http://movilzone.org/wp-content/uploads/2009/06/3_p1-150x150.jpg" class="attachment-thumbnail" alt="" title="3_p1" /></a>
</dt></dl><br style="clear: both" />
<br style='clear: both;' />
</div>
saludos