Whats the right path and image formate to put img on git-pages

whats the right path and image formate to put img on git-pages

This author gives us a hint :

she uses this link

<img src="https://images.unsplash.com/photo-1444492417251-9c84a5fa18e0?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=975&h=300&q=80"/>

but i am not able to reproduce this with a image on imgur - why
what do i need to do to achieve an image on the git-page!?

look forward to hear from you