When you add photos to a post you can find some text fields, you can fill it out or not. Some are more important than others, the best is to fill as much as possible.
What is important, and where they are visible:
- URL: the place where the photo is and do not change it.
- Title: Title appears when you go with your mouse over the image. Depending on the theme may also appear as text on the image.
- Caption: usually the text under the image (if available in theme).
- Alt Text: text when displaying the image is not possible (as replacement text).
- Description: description what is on the image. 🙂