Adding observers to boards
Teams that subscribe to Trello Business Class can add "observers" to boards within their team. Observers are board members that are able to view a board and the cards within the board, download card attachments, comment and vote on cards if that is enabled for the board, and export the board. Observers are not able to move or edit cards, upload card attachments and Observers can't change board settings.
Add a Trello member as an observer
To add someone who is already a Trello member to your board as an Observer, click "Add Members..." from the Members section of the board menu. Enter the member's username or email address. When their name populates the list select the arrow icon to the right of their name to bring up their permissions settings. Select "Observer" from this menu and they will be added to the board as an Observer.
Add a Trello member as an observer to your board.
Invite someone to Trello as an observer
To add someone who is not already a Trello member to your board as an Observer, click "Add Members..." from the Members section of the board menu. Enter the individuals email address. You will be prompted that the email address is not recognized by Trello and informed that they will be sent an invite to your board. Check the box that says "Include this member a view-only Observer?" and click "Send". When that person signs up for Trello they will automatically be added to your board as an Observer.
Invite someone to Trello as an Observer on your board.
Change a member's permissions to Observer
To change a current board member's permissions to Observer, click their avatar from the Members section of the board menu, select "Change Permissions" and select "Observer". Please note that only team admins and board admins can change a board member's permissions.
Change a board member's permissions to Observer.