Check for image size after uploading

Hi, i am using the wp_editor with the add media button in my theme for a members only area and i need to set a minimum image upload resolution for design reasons… i tried add_atachment any ideas this is what i came out to so far

function CheckImageUpload($attachmentID){
$metadata = wp_get_attachment_metadata($attachmentID);
if ($metadata[‘width’] < 560 and $metadata[‘height’] < 470)
{
wp_delete_attachment($attachmentID);
}
}

add_action( “add_attachment” , ‘CheckImageUpload’ );