create an image filter in php

my question is how can I make a query filter in mysql php I have the following

    foreach($data as $key => $img){
        $portada = @getimagesize($img['cover']);
        $w = $portada[0];
        $h = $portada[1];
        if($w >= 750 || $h >= 400){
            return $data;
        }
    }

the query has a limit of 10 of 7000 and ORDER BY rand (), I want it to only return the images that have a width greater than 750 and a height greater than 400 but this returns from everything to images that no longer exist, Where am I wrong? and thanks: D