William, you need to open the place listing on the mobile and scroll down until you find the tabs Overview, Menu, Reviews, Photos.
Then slide the tab bar to the left to see Updates. When you click it, you see By owner and By visitors below. Click By Visitors.
After that, click Add Photo Contribution at the bottom, select a photo for upload and (optionally) enter a caption.
Unfortunately the UI on my device is in German language and an old version of Maps, so Neuigkeiten should appear as Update in English and Von Besuchern as By Visitors or similar:
