Step 1: Add images to slides with Photo Slideshow Add-on.
Photo Slideshow is a free Add-on that makes it quick and easy to import an entire Google Photos or Google Drive folder into Google Slides. Once you have installed the Add-on just select either Google Photos or Google Drive and then choose the folder of images that you want to have displayed in a slideshow. Each image in the folder will automatically be placed on a slide.
There are a few things to be aware of before using the Photo Slideshow Add-on. First, it will randomly crop some images to fit into slides. Second, some images that were captured in landscape mode will be shown in portrait mode. Third, to make your slideshow automatically play in a webpage you will need to make sure that you have enabled "auto play" as illustrated in my screenshot below.
Step 2: Add music to the slideshow with the Audio Player for Slides Add-on.
AudioPlayer for Google Slides is a free Add-on that will let you add music to the background of a presentation created with Google Slides. The music that you add through the Add-on can loop in the background throughout the course of your presentation. Watch my video to learn how to use AudioPlayer for Google Slides.
As I noted in the video, you must have audio files stored in your Google Drive prior to using the AudioPlayer Add-on. It's also important to remind students to only use music that they have the rights to use for public presentations. Archive.org and the Free Music Archive are good places to find free music to use in presentations.
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