You can manually add alt text for each individual image. Or, you can add alt text at the image manager level.
Alt text added at the image manager level will automagically pre-populate the alt field every time you reuse that image.
So, when you're in a rush and you forget to type in your alt text... LibGuides does the remembering for you!
Alt text added at the image manager level is not automatically applied to images currently being used.