Since images are loaded asyncronously, we must wait to create the pdf until we actually have the image data. If we already had the jpeg image binary data loaded into a string, we create the pdf without delay.
function (imgData) {
		var doc = new jsPDF();

		doc.addImage(imgData, 'JPEG', 10, 10, 50, 50);
		doc.addImage(imgData, 'JPEG', 70, 10, 100, 120);

		doc.save('output.pdf');

	}