<?php
$filesize = $_FILES['userfile']['size'];
$filetype = $_FILES['userfile']['type'];
$type = substr($filetype, (strpos($filetype,"/"))+1);
$types=array("jpeg","gif","png");
 
if ( $filesize > 0 && $filesize <= 100000 && in_array($type, $types) ) {
// realizar acciones
}else{
echo "Imagen no valida!.";
?>