Milan Dinić

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Image descriptions are stored as content (field <code>post_content</code>) while captions are stored as excerpt (field <code>post_excerpt</code>). This means that descriptions are shown on single attachment pages, while captions are shown in <a href="https://codex.wordpress.org/Gallery_Shortcode" rel="nofollow ugc">galleries</a> and if image is embedded in a post content with a <code>[caption]</code> shortcode.
If you use images just in galleries, in order to have text below image in both places, you need to fill both fields.
This plugin changes that. You only fill description field and that text is used as caption of image in galleries.
There are no options or settings, just enable plugin and everything works automatically.

Descriptions as Captions in Galleries

Show image descriptions as captions in galleries.

nicmare

WordPress ships with a native Lightbox-Effect for image blocks. This plugin adds one tiny additional option to the core image and gallery blocks: <code>Show Caption</code>.
When the toggle is enabled, the native lightbox receives the current image alt text as a <code>data-img-alt</code> attribute on the enlarged lightbox figure. A small frontend CSS then displays that value as a caption overlay inside the lightbox image.
Please note: The caption text is taken from the image <code>alt</code> attribute.
The toggle is only available when the native Lightbox-Effect is active. If the lightbox is disabled or the image is linked somewhere else, the caption option is disabled as well.
<h3>Plugin Features</h3>
✔ adds a new toggle <code>Show caption</code> to the core Image block 
✔ adds the same toggle to the core Gallery block 
✔ the toggle can only be enabled when the native Lightbox-Effect is active 
✔ ships with German translation files for the editor toggle 
✔ uses the image <code>alt</code> attribute as value for <code>data-img-alt</code> 
✔ adds the attribute only to the enlarged image figure in the lightbox 
✔ supports galleries by passing the gallery setting to the nested image blocks 
✔ outputs the value with a lightweight frontend CSS pseudo element 
✔ uses no new block and does not replace the existing Image or Gallery blocks

LMDM Lightbox Image Caption

Adds a lightbox-only image caption toggle for core Image and Gallery blocks.

Descriptions as Captions in Galleries vs LMDM Lightbox Image Caption