This module extends the functionality provided by the Insert module, by extending the inserted markup for the image, to contain a text below the image. For all available styles, a variation with additional text is added the list of choices, and the entered description text is added to the wysiwyg where it's still editable in its own container. The inserted markup can be overridden by a template.
Take a look at the screenshots.
Install this module and the Insert module.
Create an Image field on a node, and check the "Enable Title field" option.
In the field settings, at the "insert" section, check the "Enable insert
button" field, and select the styles/presets you want to insert. Those with
the description enabled, are prefixed with a "With description" text.
Now you can enter text in the field after uploading an image into the field,
then select a style/preset with description, and the image will be inserted
with the chosen description in the WYSIWYG.