If you are tired using the same images on your screensaver again and again or you simply want to personalize it, you can use your own photos from your iPhoto library. All you have to do is flag the pictures or images you want to appear as your screensaver and unflag those which you don't want to include. This step-by-step will tell you how to use your iPhoto library as a screensaver.
1. Go to your Mac menu bar and click the Apple icon to go to 'System Preferences.' Then click the 'Desktop & Screensaver' icon on the menu bar. Locate the 'Screensaver' tab on top of the screen and click it.

2. On the 'Screensaver' page, you will see different types of animated effects for your screensaver on the left-side panel. You can present your slides in random order, cross-fade which allows images to transition smoothly in succession with each other, zoom an image back and forth to show further details, or keep your photos at the center.

3. After choosing your effects, go to the right-side panel of the screen and click 'Source.' A drop-down list will appear, click 'Photo Library' and flag the images you want to include on your screensaver. If you have more than a hundred photos in your library, you can also use it as a mosaic display.