It should be possible to allow persistent access to your device's camera in either iOS or Android.
iOS/Safari
If you click on Page Settings (the icon in the top left area of your screen next to the website URL) you should have access to your some more settings for this webpage:
Under Page Settings, you can find Website Settings and turn your Camera setting to "Allow":
Android/Chrome
To make sure Trace has permissions in Chrome, select the Site Settings > Site Settings > Camera and then Permissions. Make sure the Camera is set to Allow.