How to freeze an image on top of other images in Photoshop?

Question

Adobe Photoshop

I need to fix an image on top of other windows in Photoshop.
Like the author in the video:
https://www.youtube.com/watch?v=ncnyejtIvBc&index=...
How can this be done? As soon as I start working with another image, my reference image disappears from the workspace (because it becomes inactive).
UPD
Rebooted. Everything is working. The question can be deleted.

Answer 1

Just open two files.
You drag one to the desired corner.
These are the basics of working in Photoshop.