Hello, if you need to set the company contacts, group chat background, search box to display watermark, and Internal Group display real name, etc., administrator login in [DingTalk mobile app] - [Contacts] - [Organization Management] - [security center] set.
When turned on [Watermark for Internal Chats] the group background and the search box will add a watermark to prevent the screenshot from leaking information.
Guess you want to learn more about: How to set chatting background?