One posted by Brian where you search showimage.php for the text in bold and add what's bellow:
$thisfield = 'field' . $field['fieldid'];
if ($field['fieldid'] == 'X')
$myvarname = $field['value'];
With X being the field id number.
I've also tried every variation of the vars like $fieldid, $field[field3], $customfield, and so on because before 3.5 I was using one of them.
I remember Brian helping me out on this but I can't locate the thread now that the forums were moved here.