In order to add text to a photo, you have to hover over the image and click the pencil icon. Next, give the image a title. The title serves as the index of the image, which allows Google and other search engines to find it.
Why do I need this?
Google and other search engines can't see your images. So they just ignore them and don't index your content - Your image can't be found by google.
If you do want your image to be seen by Google and get you better search results in Google you should add text to a photo.