This, naturally, includes iPhoto. Here, you can quickly and easily transform any of your photos into your Mac’s background, and if you like a few of your images and want to use them all, you can do this as well. Once you’ve changed your background, you can access the settings for it as normal in System Preferences, where you can alter options like the menubar transparency and, if you’re using a number of your photos, how long they show onscreen.
Open up iPhoto and browse through your photos. Once you’ve found one that you like, click to select it. A yellow band should now surround the image you have chosen.
Once your image is selected, click Share in the menubar. At the bottom of the drop-down menu, click on the Set Desktop button. Your Desktop background will now instantly be changed to the photo you selected.