add fields to comments programmatically
I found my answer, see:

dsm(entity_get_info());
dsm(field_info_bundles());


so my code should be:

$instance = array(
    'field_name' =&gt; 'field_image',
    'entity_type' =&gt; 'comment',
    'bundle' =&gt; 'comment_node_article',
    'label' =&gt; t('Images'),
    ....