$re = '/<img[^>]*(?=\"https?:\/\/(www\.)?urpgstatic\.com)\"([^\"]*)\"[^>]*>/m';
$str = '<img src="https://www.pokeyplay.com/imagenes/backend/publicidad.gif" alt="Publicidad" align="left" />
<img src="https://www.pokeyplay.com/imagenes/backend/spacer.gif" alt="sp" />
<img src="imagenes/backend/etiqueta-pyp-pokedex.gif" alt="P&P PokéDex" width="184" height="100" />
<img src="imagenes/backend/spacer.gif" alt="sp" />
<img src="http://urpgstatic.com/img_library/pokemon_sprites/187.png" style="vertical-align:middle" />
<img src="https://urpgstatic.com/images/pokemon-home.png" alt="UnovaRPG (formerly Pokémon Indigo) - Online Pokemon Game" width="250" height="272">';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php