Open this page on a computer or tablet and ensure that the "Test" target to the right is fully visible. Open a QR code reader on your smartphone, usually built in to the camera app, and scan the target. Open the link from the QR code in either Safari (iPhone) or Chrome (Android) to start the viewer. Keep your camera pointed to the target and the AR image will appear.
Tips
ARcostume, the ARcostume target design, and the ARcostume viewer app are copyright 2018, GreenZeta by Matthew Wilber. Do to the experiemental nature of the AR app, results of the viewer app may vary between devices. The ARcostume shirt is printed and shipped by a third party, RedBubble. RedBubble provides their own terms and conditions that are separate from the ARcostume site and viewer app. Direct any issues regarting the t-shirt, it's material or the printed image to RedBubble support.