GiantZOC

//https://stackoverflow.com/questions/18299806/how-to-check-file-mime-type-with-javascript-before-upload/29672957#29672957
	// Return the first few bytes of the file as a hex string
	function getBLOBFileHeader(url, blob, callback) {
		var fileReader = new FileReader();
		fileReader.onloadend = function (e) {
			var arr = (new Uint8Array(e.target.result)).subarray(0, 4);
			var header = "";
			for (var i = 0; i < arr.length; i++) {
				header += pad(arr[i].toString(16), 2);