thumbs jpeg, gif, png

[telegio]

http://www.asciitable.it/mimetypes.asp

io farei così
$estensione1 = "image/pjpeg"; //Jpeg type 1
$estensione2 = "image/jpeg"; //Jpeg type 2
$estensione3 = "image/gif"; //Gif type
$estensione4 = "image/png"; //Png type

if ($_FILES['img1']['type'] == $estensione1 or $_FILES['img1']['type'] == $estensione2) {
$img = @imagecreatefromjpeg( "{$pathToImages}{$fname}" );
} elseif ($_FILES['img1']['type'] == $estensione3) {
$img = @imagecreatefromgif( "{$pathToImages}{$fname}" );
} elseif ($_FILES['img1']['type'] == $estensione4) {
$img = @imagecreatefrompng( "{$pathToImages}{$fname}" );
} else {
echo "estensione errata";
}