Instructions on how to take a photo and make it your screen saver
Need instruction on how to make a photo i took into my Screensaver on my Mac
iMac 24″, macOS 12.3
Do you mean desktop image or screen saver?
Customise the screen saver on your Mac in the support document Use a screen saver on your Mac describes how to choose images as a screensaver.
Also, you can use your picture as a desktop image. Customise the desktop picture on your Mac explains the steps to achieve this.