The Caption dialog creates caption boxes on images with options for text color, padding and alignment and caption container margin, padding, background color and border styling.
In its simplest form, this consists of a parent <span> wrapped around the source image and an additional text <span>, eg:
<span class="wf_caption" style="max-width: 300px; display: block; width: 100%; border: 1px solid #000000; background-color: #eeeeee;">
<img alt="flower" src="https://cdn.joomlacontenteditor.net/images/nature.jpg" />
<span style="text-align: center; display: block;">Nature</span>
</span>
Example:
Nature