The images that previously showed when creating a web app on a mobile device (for example saving the forum to home screen on an iPhone) or when saving to the bookmark favourites that previous appeared with my forum when on self hosting no longer appear, they were previously uploaded via FTP.

Where within the admin section can I add these images? I can see favicon and share images which are there but not where to add the others. 

Thanks

Check out System>Settings>Web App, which is what I believe you are looking for