ulitmate wp query search filter

add_filter('uwpqsf_form_bottom', 'exclude_cmf');
function exclude_cmf(){
$i= '100';// number in the array of meta field, must greater than your meta field filter number.
$metakey = '_thumbnail_id';//your meta key
echo '<input type="hidden" name="cmf['.$i.'][metakey]" value="'.$metakey.'"/>';
echo '<input type="hidden" name="cmf['.$i.'][compare]" value="2"/>';
echo '<input type="hidden" name="cmf['.$i.'][value]" value="uwpqsfcmfall"/>';
}