从数据库中的数组创建有效的JSON

I'm trying to put my data into Json format. The code seems to work fine, I get a Json format, but the data is not Json valid. This is how the json comes out:

({
"sample": [
    {
        "0": "12",
        "image_id": "12",
        "1": "background.JPG",
        "path": "background.JPG",
        "2": "background.JPG",
        "name": "background.JPG",
        "3": "image\/jpeg",
        "type": "image\/jpeg",
        "4": "51600",
        "size": "51600",
        "5": "4",
        "likes": "4",
        "6": "zwitserland",
        "onderwerp": "zwitserland",
        "7": "Landscape from cableway",
        "beschrijving": "Landscape from cableway"
    },
    {
        "0": "13",
        "image_id": "13",
        "1": "IMG_1052.JPG",
        "path": "IMG_1052.JPG",
        "2": "IMG_1052.JPG",
        "name": "IMG_1052.JPG",
        "3": "image\/jpeg",
        "type": "image\/jpeg",
        "4": "45434",
        "size": "45434",
        "5": "28",
        "likes": "28",
        "6": "belgium",
        "onderwerp": "belgium",
        "7": "Highway in Belgium",
        "beschrijving": "Highway in Belgium"
    }, ETC ETC

This is my php code. When I put my code into a Json editor I get the following error:

Parse error on line 1: ({ "sample": [ ^ Expecting '{', '['

$arr = array();
$rs = mysql_query("SELECT * FROM images");

while($obj = mysql_fetch_array($rs)) {
$arr[] = $obj;

}
$json = '{"sample":'.json_encode($arr).'}';
echo $_GET['jsoncallback'] . '(' . $json . ')';

You shouldn't try manually building your own JSON, for reasons exactly like this.

Use this and this alone.

$json = json_encode(array("sample" => $arr));

Or

$json = json_encode(array("sample" => array($_GET["jsoncallback"] => $arr)));