Question regarding updating the Blog testimonial widget

Hi there Fortuna Support Team!

May I ask how do you calculate the ID of the profile pic used on the Blog testimonial widget (part of the Fortuna Default Sidebar).

Here’s is a screenshot of a profile pic ID in the widget. I can’t seem to change the pictures using standard URLs. I’m surely missing something.

https://www.dropbox.com/s/vy2d7izkaupqgz7/Fortuna%20widget.png?dl=0

Thanks in advance for your help!