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You can use the 'wp_get_attachment_image_attributes' hook

add_filter(
    'wp_get_attachment_image_attributes',
    'image_attributes',
    20,
    2
);
function image_attributes( $attr, $attachment )
{
    // Get post parent
    $parent = get_post_field( 'post_parent', $attachment );
    
    // Get post title
    $title = get_post_field( 'post_title', $parent );
    
    if ( is_single( $parent ) ) {
        $attr['alt']=$title;
    }
    
    return $attr;
}

Or Check Out my new plugin

Its now on WordPress plugins directory. The Alt Manager plugin is a simple plugin that changes images Alt and Title attributes text on your (Pages – Posts) separately to your website name or (post or page) title.This Plugin bulk changes images Alt and Title attributes immediately you dont need to change image info on media library. https://wordpress.org/plugins/alt-manager/

You can use the 'wp_get_attachment_image_attributes' hook

add_filter(
    'wp_get_attachment_image_attributes',
    'image_attributes',
    20,
    2
);
function image_attributes( $attr, $attachment )
{
    // Get post parent
    $parent = get_post_field( 'post_parent', $attachment );
    
    // Get post title
    $title = get_post_field( 'post_title', $parent );
    
    if ( is_single( $parent ) ) {
        $attr['alt']=$title;
    }
    
    return $attr;
}

Or use this plugin

Alt Manager WordPress plugin bulk changes WordPress images Alt and Title attributes text and generate empty values on your (Homepage – Pages – Posts – Blog )[Free Version] (Products – Shop page – Custom Post Type – Custom Post Type archive page)[Premium Version] separately to several dynamic related values, This plugin is a full solution for generating alt and title values.

This Plugin bulk changes images Alt and Title attributes immediately on your website front end, you don’t need to change image info on media library. https://wordpress.org/plugins/alt-manager/

You can use the 'wp_get_attachment_image_attributes' hook

add_filter(
    'wp_get_attachment_image_attributes',
    'image_attributes',
    20,
    10
);
    function image_attributes( $attr, $attachment )
    {
        // Get post parent
        $parent = get_post_field( 'post_parent', $attachment );
        // Get post title
        $title = get_post_field( 'post_title', $parent );
    if ( is_single( $parent ) ) {
    $attr['alt']=$title;
    }
    return $attr;
    }

Or Check Out my new plugin

Its now on WordPress plugins directory. The Alt Manager plugin is a simple plugin that changes images Alt and Title attributes text on your (Pages – Posts) separately to your website name or (post or page) title.This Plugin bulk changes images Alt and Title attributes immediately you dont need to change image info on media library. https://wordpress.org/plugins/alt-manager/

You can use the 'wp_get_attachment_image_attributes' hook

add_filter(
    'wp_get_attachment_image_attributes',
    'image_attributes',
    20,
    2
);
function image_attributes( $attr, $attachment )
{
    // Get post parent
    $parent = get_post_field( 'post_parent', $attachment );
     
    // Get post title
    $title = get_post_field( 'post_title', $parent );
    
    if ( is_single( $parent ) ) {
        $attr['alt']=$title;
    }
    
    return $attr;
}

Or Check Out my new plugin

Its now on WordPress plugins directory. The Alt Manager plugin is a simple plugin that changes images Alt and Title attributes text on your (Pages – Posts) separately to your website name or (post or page) title.This Plugin bulk changes images Alt and Title attributes immediately you dont need to change image info on media library. https://wordpress.org/plugins/alt-manager/

Check Out my new plugin

Its now on WordPress plugins directory. The Alt Manager plugin is a simple plugin that changes images Alt and Title attributes text on your (Pages – Posts) separately to your website name or (post or page) title.This Plugin bulk changes images Alt and Title attributes immediately you dont need to change image info on media library. https://wordpress.org/plugins/alt-manager/

You can use the 'wp_get_attachment_image_attributes' hook

add_filter(
    'wp_get_attachment_image_attributes',
    'image_attributes',
    20,
    10
);
    function image_attributes( $attr, $attachment )
    {
        // Get post parent
        $parent = get_post_field( 'post_parent', $attachment );
        // Get post title
        $title = get_post_field( 'post_title', $parent );
    if ( is_single( $parent ) ) {
    $attr['alt']=$title;
    }
    return $attr;
    }

Or Check Out my new plugin

Its now on WordPress plugins directory. The Alt Manager plugin is a simple plugin that changes images Alt and Title attributes text on your (Pages – Posts) separately to your website name or (post or page) title.This Plugin bulk changes images Alt and Title attributes immediately you dont need to change image info on media library. https://wordpress.org/plugins/alt-manager/