External drives take a few moments to become available after you log in to your Mac. As a result, desktop pictures stored on external drives might not load automatically when your desktop appears. Your Mac then uses one of the desktop pictures included with your Mac instead.
For best results, use desktop pictures that are stored on your internal hard drive. For example, you can copy images to the Pictures folder of your home folder, then use Desktop & Screen Saver preferences to choose images from that folder:
- From the Apple menu, choose System Preferences, then click Desktop & Screen Saver.
- Click the Desktop tab.
- Select your Pictures folder from the list of folders on the left. The images in that folder appear on the right.
If you don't see the folder containing your images, click the Add button, then choose the folder.
- Click the image that you want to use as your desktop picture.