You can add captions to your images by using the “Image Caption” field in the “Add an Image” or the “Edit Image” window.
1) When you add a caption to an image, caption shortcode is inserted into the source code.
2) The caption is also used as the alternate text for the image by default. Here is the source code for the image above right after inserting it.
The “Add an Image” window let’s you upload an image and give it a title, caption, description, alignment, and size. These fields are used on the permalink page for the image.