Desktop preferences
Use the Desktop pane of Desktop & Screen Saver System Preferences to choose a different pattern, color, or picture for the desktop (the background area of your screen).
To open this pane, choose Apple menu > System Preferences, click Desktop & Screen Saver, then click Desktop.
List of folders, images, and pictures | Select a folder or set of pictures from the list on the left, then click a pattern or picture on the right. If you don’t see anything when you select the Pictures folder, either you don’t have pictures in that folder or the pictures don’t have the right file format—JPEG, PICT, TIFF, or PNG. 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 1024 x 768 pixels. |
Add | To use an image from another folder, click the Add button To remove a folder you added, select it, then click the Remove button |
Fill Screen pop-up menu | When you select a picture from Photos or the Pictures folder, choose how you want to arrange it on the screen—for example, fill the screen or center the picture. Some choices may distort the picture. |
Change picture | Cycle through all the pictures available in the item or folder you selected in the list on the left. Use the pop-up menu to choose how often to change the picture; for example, every hour. This option may affect the performance of some apps, such as games, that use many graphics. |
Random order | When you choose to change pictures, you can also select to display the pictures in a random order. |
Translucent menu bar (not available on all computers) | Make the desktop color or picture visible behind the menu bar along the top of the screen. |
and Remove 