EntityFieldQuery: number of field values as condition
Seems like stating the obvious but you need to count the number of values in 'field_images', then you can set the condition to check that result and make sure it is greater than 0.

There's a good overview of adding expressions and conditions with the count() function on this question.

You'll also need to perform a join between 'node' and the table that holds your field values before you make your count, something like this:

$query = db_select('node', 'n');
$query-&gt;join('field_images', 'fi', 'n.nid = fi.nid');
...rest of query