WordPress Blog Thumbnail API — Auto-Generate Featured Images From Any Post Title

Every WordPress post needs a featured image. The default workflow — open Canva, drop the title into a template, export a 1200×630 PNG, upload it to the Media Library, set it as featured — takes ten to twenty minutes per post. For blogs shipping two or three times a week, it's the reason posts sit in Draft for days.

This page is the WordPress-specific version of the fix. The official ThumbAPI WordPress plugin drops a Generate button into every post sidebar; one click and a 1200×630 cover lands in the Media Library and gets set as the featured image. If you'd rather wire it in code, the REST endpoint works from wp_remote_post() or any small must-use plugin — same API, same result. Every claim below is grounded in the real plugin and the real endpoint — no invented features.

What It Does

• Featured image on demand.One button in the post sidebar → a 1200×630 cover generated from the post title, uploaded to the Media Library, and set as the post's featured image.
• Three visual styles. Faceless (default), With Image (personal photo overlay), or With Logo (brand overlay). Toggle per post or set a channel default.
• 13 category hints. Bias the AI style with tech-saas, business-finance, education-tutorial, and 10 more so the cover matches the post's niche.
• WebP or PNG output. WebP by default (~40% smaller); PNG for legacy pipelines that need broad compatibility.

How It Works

Three steps. Under 30 seconds from clicking Generate to seeing the cover in the sidebar.

1. Write a title. Save the draft.
2. Click Generate in the ThumbAPI sidebar panel (block editor) or the ThumbAPI meta box (classic editor). Pick a style and a category.
3. Cover appears.The generated 1200×630 image uploads to the Media Library and is set as the post's featured image automatically.

Behind the panel, WordPress calls the ThumbAPI /v1/generate endpoint with the title and options. For the raw REST integration (bypassing the plugin), the shape is the same as the Node.js integration guide — one fetch, one JSON payload:

<?php
add_action( 'save_post', function ( $post_id, $post ) {
    if ( has_post_thumbnail( $post_id ) ) return;
    if ( $post->post_status !== 'publish' ) return;

    $res = wp_remote_post( 'https://api.thumbapi.dev/v1/generate', [
        'headers' => [
            'x-api-key' => THUMBAPI_KEY,
            'Content-Type' => 'application/json',
        ],
        'body' => wp_json_encode( [
            'title' => get_the_title( $post_id ),
            'format' => 'blogpost',
            'outputFormat' => 'png',
        ] ),
        'timeout' => 40,
    ] );

    if ( is_wp_error( $res ) ) return;

    $data = json_decode( wp_remote_retrieve_body( $res ), true );
    $png = base64_decode( explode( ',', $data['image'] )[1] );

    $upload = wp_upload_bits( sanitize_title( $post->post_name ) . '.png', null, $png );
    if ( $upload['error'] ) return;

    $attach_id = wp_insert_attachment( [
        'post_mime_type' => 'image/png',
        'post_title' => $post->post_title,
        'post_status' => 'inherit',
    ], $upload['file'], $post_id );

    require_once ABSPATH . 'wp-admin/includes/image.php';
    $meta = wp_generate_attachment_metadata( $attach_id, $upload['file'] );
    wp_update_attachment_metadata( $attach_id, $meta );
    set_post_thumbnail( $post_id, $attach_id );
}, 10, 2 );

Drop the file in wp-content/mu-plugins/, set THUMBAPI_KEY in wp-config.php, and every published post without a featured image gets one automatically. For the plugin version (no code), install "ThumbAPI" from WordPress.org — full walkthrough on the WordPress integration page.

Use Cases

• Solo bloggers publishing weekly. Every new post ships with a unique cover — no design queue, no template drift.
• Multi-author WordPress sites. Contributors hit Publish and the cover just exists. See the automated blog covers use case for the deeper pipeline (Ghost, Sanity, Contentful use the same shape).
• Agencies running WordPress client sites. Deploy the plugin across every client, set per-client brand logos, and stop billing hours for cover design.
• Blogs migrating off Squarespace/Ghost onto WordPress. Backfill the whole archive with the bulk thumbnail generation script — one CSV in, a folder of PNGs out.

Pricing

Pricing is metered in credits. A standard 1200×630 blog cover costs 10 credits. Add+2 credits per call for a saved logo overlay, another +2 for a custom reference set.

Free tier output carries a small watermark; Creator and up are watermark-free. See full pricing details.

Customisation Parameters

Related Reading

• ThumbAPI WordPress plugin — the no-code path, install from WordPress.org.
• Automated blog covers use case — same pipeline for Ghost, Sanity, Contentful, and any headless CMS.
• Blog Cover API landing page — the format-focused hub, formats and pricing in one place.
• Thumbnail API with Node.js guide — for headless WordPress setups running Node in the middle.

FAQ