imagecopy 等函数报错，需要的是资源类型，给的却是布尔值

由于爬取的图片mime值不一样，imagecreatefrom***时要用不同的函数获取，与mime值对应

demo：

$size = getimagesize('./cleanWaterText/20190318/'.$v);
$mime = $size['mime'];

switch ($mime) {
    case 'image/png':
        $source = imagecreatefrompng('./cleanWaterText/20190318/'.$v);
        echo "ispng";
    break;
    case 'image/jpeg':
        $source = imagecreatefromjpeg('./cleanWaterText/20190318/'.$v);
        echo "is jpeg";
    break;
        case 'image/gif':
        $source = imagecreatefromgif('./cleanWaterText/20190318/'.$v);
    break;

    default:
        # code...
    break;
}