wpcocktail

The Site Title Caption Modifier is a simple WordPress plugin that sets the caption of all images in your WordPress site to the site title. This is particularly useful for maintaining a consistent branding or style across all posts and pages. The plugin works by hooking into the WordPress ‘img_caption_shortcode’ filter and modifying the caption output.

Image Caption for WP

Automatically sets the caption of all images to your site's title.

Jens Hunt

Image Caption on Featured adds the image caption on the featured image. The caption appears as a headline on the image.
See how to use it at: http://www.jenshunt.se/image-caption-on-featured-wordpress-plugin/

Image Caption on Featured

Image Caption on Featured adds the caption on the featured image.

Image Caption for WP vs Image Caption on Featured