Error Upload JPG ó jpg

[prcarreno]

if($_FILES['imagen']['tmp_name']){
//rename($_FILES['imagen']['name'], strtolower($_FILES['imagen']['name']));
echo $_FILES['imagen']['name'];
echo "<br>";
$_FILES['imagen']['name'] = strtolower($_FILES['imagen']['name']);
echo $_FILES['imagen']['name'];
$dir_new_g = '../data/categoria_seccion/g'.date("Ymd_His").strtolower($_FILES['imagen']['name']);
$dir_new_c = '../data/categoria_seccion/c'.date("Ymd_His").strtolower($_FILES['imagen']['name']);

$img = new ResizePicture($_FILES['imagen']['tmp_name']);
$tam = $img -> getWidth();
if($tam > 610){
$tama = 610;
}else{
$tama = $tam;
}
cambiar_segun_ancho($_FILES['imagen']['tmp_name'],$dir_new_g,$tama);
cambiar_alto_y_ancho($_FILES['imagen']['tmp_name'],$dir_new_c,90,90);
}


Ahi esta el codigo :)