Is there a way to filter posts by featured image when initialising a WP_Query object?
$my_query = WP_Query(array("has_thumbnail"=>true));
or, more ideally
$my_query = WP_Query(array("has_thumbnail_size"=>"custom_size"));
Technically featured image is custom field with name
Size on other hand is attribute of that attachment and not post itself. You will need to loop through attachment and get sizes they have (if I remember right it should be in data returned by