Right.
I couldn't find a definitive answer to this question anywhere, so here is my solution:
Text Formatted Code
$_CONF['advanced_editor'] = true;
Option 2: Add the following line to your config.php in the admin_html section
Text Formatted Code
'img' => array('class' => 1, 'id' => 1, 'align' => 1, 'src' => 1, 'width' => 1, 'height' => 1, 'alt' => 1),
If it is the last line of the array then you want to remove the last comma. If it is not the last line then leave the trailing comma in. The bottom line should have no comma, and every other line should have one. eg:
Text Formatted Code
$_CONF['admin_html'] = array (
'p' => array('class' => 1, 'id' => 1, 'align' => 1),
'div' => array('class' => 1, 'id' => 1),
'span' => array('class' => 1, 'id' => 1),
'table' => array('class' => 1, 'id' => 1, 'width' => 1, 'border' => 1,
'cellspacing' => 1, 'cellpadding' => 1),
'tr' => array('class' => 1, 'id' => 1, 'align' => 1, 'valign' => 1),
'th' => array('class' => 1, 'id' => 1, 'align' => 1, 'valign' => 1,
'colspan' => 1, 'rowspan' => 1),
'td' => array('class' => 1, 'id' => 1, 'align' => 1, 'valign' => 1,
'colspan' => 1, 'rowspan' => 1),
'img' => array('class' => 1, 'id' => 1, 'align' => 1, 'src' => 1, 'width' => 1, 'height' => 1, 'alt' => 1)
);