How to overlay pictures on the outline of another picture?

Question

Adobe Photoshop

Haven't used it for a long time. Can't remember hotkeys. There is a standard quadrangular picture, and it is necessary to impose it on top of another non-standard picture shape. How to fill the background in it.

Answer 1

Image and mask on 2 layers, the layer mask should be the underlying one. RMB on the layer to be clipped -> "clipping mask".

Answer 2

Alt + left click between layer icons. Or create a mask.