Yealink SIP-T48S User Manual page 91

You can click Delete Photo to delete the custom photo.
The phone only supports *.png, *.jpg and .bmp format files. The file size must be less than 5M.
Note
You can only delete custom photos.
To change the custom photo for the contact via web user interface:
Click on Directory->Local Directory.
1.
Click the desired entry you want to edit.
2.
Select the desired photo from the pull-down list of Photo.
3.
Click Edit to accept the change.
4.
Customizing Your Phone
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