Customise the desktop picture on your Mac
You can choose the picture that’s displayed on your desktop. Your Mac comes with dozens of desktop pictures to choose from, or you can use your own pictures or choose a solid colour.
Tip: You can drag an image from your desktop or a folder onto the thumbnail at the top of the pane to use the image as your desktop picture.
On your Mac, choose Apple menu
On the left, find a picture or colour:
Pictures and colours that come with your Mac: Click the arrow
next to Apple, then select a folder, such as Desktop Pictures or Colours, to see thumbnails of available pictures or colours.Dynamic desktop pictures can automatically change throughout the course of the day based on your current location. If Location Services is turned off in Privacy preferences, the picture changes based on the time zone specified in Date & Time preferences.
Some dynamic desktop pictures may also provide still images so the desktop picture doesn’t distract from the light or dark appearance. For example, if you chose the dark appearance during macOS setup, the desktop picture is set to a dark still image. To use or stop using a still image (if available), click the pop-up menu, then choose an option.
Your pictures: Click the arrow
next to Photos (or iPhoto if available). If your pictures are in the Pictures or another folder, click the arrow next to Folders, then select a folder.To add a folder, click the Add button
, navigate to and select the folder, then click Choose.If you don’t see anything when you select the folder that contains your pictures, they might not have the right file format — JPEG, PICT, TIFF, PNG or HEIC. To change a picture’s format, open it in the Preview app, then save it in the new format. If pictures look fuzzy, try using larger ones, such as 1024x768 pixels.
On the right, click the picture you want to use.
The desktop immediately changes, so you can see how the picture looks. When you use one of your own pictures, you can choose to have it fill the screen, be centred or otherwise arranged. It’s easy to click around and try different pictures and arrangements until you find the one you like best.
To use all the pictures in a folder, select the “Change picture” tick box, then choose how often you want the picture to change — for example, every hour. The pictures are shown in the order they appear in the folder, or you can choose to show them in a random order.
To quickly use a picture you have in the Photos app, select the picture in Photos, click the Share button 
in the Photos toolbar, then choose Set Desktop Picture.
You can use a picture you see on the web as your desktop picture. Control-click the image in the browser window, then select Use Image as Desktop Picture.