Automatically Add Caption in image

I want to automatically add caption for each picture appears in the name of the image or the alternative text

example Caption add automatic

You can add programmatically caption, alt, description every time you upload image at backend.

Automatically Set the WordPress Image Title, Alt-Text & Other Meta

I tried myself this and worked nice as your expectation. This is for all your future upload images.

Try this and let me know.

/* Automatically set the image Title, Alt-Text, Caption & Description upon upload
--------------------------------------------------------------------------------------*/
add_action( 'add_attachment', 'my_set_image_meta_upon_image_upload' );
function my_set_image_meta_upon_image_upload( $post_ID ) {

    // Check if uploaded file is an image, else do nothing

    if ( wp_attachment_is_image( $post_ID ) ) {

        $my_image_title = get_post( $post_ID )->post_title;

        // Sanitize the title:  remove hyphens, underscores & extra spaces:
        $my_image_title = preg_replace( '%\s*[-_\s]+\s*%', ' ',  $my_image_title );

        // Sanitize the title:  capitalize first letter of every word (other letters lower case):
        $my_image_title = ucwords( strtolower( $my_image_title ) );

        // Create an array with the image meta (Title, Caption, Description) to be updated
        // Note:  comment out the Excerpt/Caption or Content/Description lines if not needed
        $my_image_meta = array(
            'ID'        => $post_ID,            // Specify the image (ID) to be updated
            'post_title'    => $my_image_title,     // Set image Title to sanitized title
            'post_excerpt'  => $my_image_title,     // Set image Caption (Excerpt) to sanitized title
            'post_content'  => $my_image_title,     // Set image Description (Content) to sanitized title
        );

        // Set the image Alt-Text
        update_post_meta( $post_ID, '_wp_attachment_image_alt', $my_image_title );

        // Set the image meta (e.g. Title, Excerpt, Content)
        wp_update_post( $my_image_meta );

    } 
}