Insert image tag in checkboxes list
You should be able to add a prefix or suffix with the field. See Field Suffix in the Form API, So your code might be:

$form['copy'] = array(
'#type' =&gt;'checkbox', 
'#title' =&gt; t('my taxonomy term.'),
'#field_suffix' =&gt; '&lt;img src="myimg.png" /&gt;',
);


You can use field_prefix if you want it to come before.