I supplied a “User Card Background Image” even though I have no idea what that is.
Here in this reply you will see my face as my profile picture, left to my username. Click once on my username with your left mouse button. The pop-up you see, contains the profile card background.
Yup, I figured it out half a second after posting and you replied even as I was in the process of deleting it! So, I’ll just mark it solved instead.