If the user doesn't expect to see a different image, that is not from the user. Then, the account used by this Teacher is not linked to any Staff Information Account.
The admin can verify if the account used by this staff is not linked to any Staff Information by using the function called Add/Edit Users. Add/Edit User is under Staff Management.
Inside Add/Edit User:
1. Please search for the user name of the Teacher/User.
2. Once you have seen the user name of the Teacher. Please check the column called Staff.
3. Under the column name called Staff, you can see if any Staff Information is indicated.
4. If the staff column shown under the Teacher is {none} , it means that the user name is not linked to Staff Information.
This screenshot shows where the Staff column is located. The screenshot shows also that some staffs are not linked to any Staff Information. To be specific Staff Name Hon, Intern, phdemo and Eunice is not linked as it shows {none}. Information shown in the screenshot is for example only. 
If the Admin verified that the Teacher Account is not linked. Please click this for more information.
In future, please create a Teacher Account using Staff Information Settings to avoid similar issues.