There are situations when uploading a profile image is optional. For that sort of situation, there is a solution that will help you enable default pictures for every user who didn’t upload their profile picture.
Follow these steps:
Navigate to Signature Management and open the Widgets (drag-and-drop) editor.
Drag the Profile Photo widget into your signature template..
From Visibility section elect your preferred fallback option:
Use Company Logo if Photo is missing
Use Custom Image if Photo is missing