AS3 – Image detection with unknow file type extention.

Here is a function wich check if a file is an image or not.
The file type is determined following the signing of the header.

//------------------------------------------------------------------------------------------------------
// AS3/AIR Image detection with unknow file type extention.
// V 1.0
//------------------------------------------------------------------------------------------------------
public function GetImageFileType(TestFile : File) : String {
	var extention : String     = "";
        var Bytes     : ByteArray  = new ByteArray();
	var BmpStream : FileStream = new FileStream();
	Bytes.endian = Endian.LITTLE_ENDIAN;
	BmpStream.open(TestFile, FileMode.READ);
	BmpStream.position = 0;
	BmpStream.readBytes(Bytes, 0, 8 );
	BmpStream.close();
	//-------------------------------------------------------
	var signature : int = Bytes.readShort();
	if (signature == 0x4D42) {
		extention = "bmp";
	} else {
		Bytes.position = 0;
		signature = Bytes.readInt()& 0xFFFFFF;
		if (signature == 0xFFD8FF) {
			extention = "jpg";
		} else {
			Bytes.position = 0;
			signature = Bytes.readInt()& 0xFFFFFFFF;
			if (signature == 0x38464947  ) {
				extention = "gif";
			} else {
				Bytes.position = 0;
				signature = Bytes.readInt();
				if (signature == 0x474E5089 ) {
					signature = Bytes.readInt();
					if (signature == 0x0A1A0A0D ) {
						extention = "png";
					}
				}
			}
		}
	}
        return extention;
}