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ZeroByteCode
ZeroByteCode

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How to Create an AI Featured Image Generator WordPress Plugin

Creating custom WordPress plugins can significantly enhance your website's functionality.

One exciting application is generating featured images for posts using artificial intelligence.

The ZeroByteCode AI Featured Image Generator plugin utilizes OpenAI's Dall-E 3 API to automatically create stunning images based on the content of your posts.

This article will guide you through the process of developing this plugin, highlighting each component and its purpose.

Overview of the Plugin

The ZeroByteCode AI Featured Image Generator plugin simplifies the process of generating and setting featured images for WordPress posts. It includes:

  1. An admin options page for configuring settings.
  2. A meta box in the post editor for generating featured images.
  3. Integration with the OpenAI API to generate images based on post content.
  4. Secure handling of API keys and user permissions.

Step 1: Setting Up the Plugin

Plugin Header and Security

Every WordPress plugin starts with a header that provides metadata about the plugin, such as its name, description, and version.

Additionally, it's crucial to include a security check to prevent direct access to the plugin file.

/*
* Plugin Name:       ZeroByteCode AI Featured Image Generator
* Plugin URI:        https://zerobytecode.com/create-a-wordpress-plugin-to-generate-featured-images-using-ai/
* Description:       One-click generate and set WordPress post featured image using OpenAI's Dalle 3 AI.
* Version:           1.0
* Author:            ZeroByteCode
* Author URI:        https://zerobytecode.com/
* Text Domain:       zerobytecode
*/

// If this file is called directly, abort.
if (!defined('WPINC')) {
    die;
}
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Step 2: Registering the Options Page

The options page allows administrators to enter the OpenAI API key and configure the content template for generating image prompts.

Registering the Options Page 

function zerobytecode_register_options_page()
{
    add_options_page(
        __('ZeroByteCode Featured Image Generator Settings', 'zerobytecode'),
        __('ZeroByteCode AI', 'zerobytecode'),
        'manage_options',
        'zerobytecode-ai-settings',
        'zerobytecode_options_page_html'
    );
}
add_action('admin_menu', 'zerobytecode_register_options_page');
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Activating Default Options

When the plugin is activated, default settings, such as the content template, are set.

function zerobytecode_activate_plugin()
{
    $default_template = 'Based on the user’s input, you must generate a single sentence, detailed prompt to generate an image using an AI image generation. The image is the thumbnail for the blog post, and the content the user passes in is portions of that blog post. Distill a single concept or topic based on the user’s input, then create the prompt for image generation.';

    if (get_option('zerobytecode_content_template') === false) {
        update_option('zerobytecode_content_template', $default_template);
    }
}
register_activation_hook(__FILE__, 'zerobytecode_activate_plugin');
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Options Page HTML

This function renders the HTML for the plugin's settings page.

function zerobytecode_options_page_html()
{
    if (!current_user_can('manage_options')) {
        return;
    }

    if (isset($_GET['settings-updated'])) {
        add_settings_error('zerobytecode_messages', 'zerobytecode_message', __('Settings Saved', 'zerobytecode'), 'updated');
    }

    settings_errors('zerobytecode_messages');
?>
    <div class="wrap">
        <h1><?php echo esc_html(get_admin_page_title()); ?></h1>
        <form action="options.php" method="post">
            <?php
            settings_fields('zerobytecode_settings');
            do_settings_sections('zerobytecode-ai-settings');
            submit_button(__('Save Settings', 'zerobytecode'));
            ?>
        </form>
    </div>
<?php
}
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Step 3: Registering the Settings

Settings registration is essential for managing and storing options like API keys and content templates.

function zerobytecode_register_settings()
{
    register_setting('zerobytecode_settings', 'zerobytecode_openai_api_key', 'sanitize_text_field');
    register_setting('zerobytecode_settings', 'zerobytecode_content_template', 'sanitize_textarea_field');

    add_settings_section(
        'zerobytecode_settings_section',
        __('OpenAI API Settings', 'zerobytecode'),
        'zerobytecode_settings_section_callback',
        'zerobytecode-ai-settings'
    );

    add_settings_field(
        'zerobytecode_openai_api_key',
        __('OpenAI API Key', 'zerobytecode'),
        'zerobytecode_openai_api_key_render',
        'zerobytecode-ai-settings',
        'zerobytecode_settings_section'
    );

    add_settings_field(
        'zerobytecode_content_template',
        __('Content Template', 'zerobytecode'),
        'zerobytecode_content_template_render',
        'zerobytecode-ai-settings',
        'zerobytecode_settings_section'
    );
}
add_action('admin_init', 'zerobytecode_register_settings');

function zerobytecode_settings_section_callback()
{
    echo '<p>' . __('Enter your OpenAI API settings below.', 'zerobytecode') . '</p>';
}

function zerobytecode_openai_api_key_render()
{
    $openai_api_key = get_option('zerobytecode_openai_api_key');
?>
    <input type="text" name="zerobytecode_openai_api_key" value="<?php echo esc_attr($openai_api_key); ?>" size="50">
<?php
}
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Step 4: Enqueuing Admin Scripts

The plugin includes JavaScript for the admin interface, enabling the "Generate Image" button functionality.

function zerobytecode_enqueue_scripts($hook)
{
    if (!in_array($hook, ['post.php', 'post-new.php'], true)) {
        return;
    }

    wp_enqueue_script(
        'zerobytecode-admin-js',
        plugin_dir_url(__FILE__) . 'js/admin.js',
        ['jquery'],
        '1.0',
        true
    );

    wp_localize_script('zerobytecode-admin-js', 'zerobytecode', [
        'nonce' => wp_create_nonce('wp_rest'),
        'rest_url' => '/zerobytecode/v1/generate-image/'
    ]);
}
add_action('admin_enqueue_scripts', 'zerobytecode_enqueue_scripts');
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Step 5: Meta Box for Generating Images

The meta box provides a user interface for generating the featured image within the post editor.

function zerobytecode_register_meta_box()
{
    add_meta_box(
        'zerobytecode_featured_image_generator',
        __('Generate Featured Image', 'zerobytecode'),
        'zerobytecode_display_generator_button',
        null,
        'side',
        'high'
    );
}
add_action('add_meta_boxes', 'zerobytecode_register_meta_box');

function zerobytecode_display_generator_button($post)
{
    echo '<button type="button" id="zerobytecode_generate_btn" data-postid="' . esc_attr($post->ID) . '" class="button button-primary button-large">' . __('Generate Image', 'zerobytecode') . '</button>';
}
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Step 6: REST API Integration

The REST API handles requests to generate images using OpenAI's Dall-E 3 API.

Registering the REST Route 

function zerobytecode_register_rest_route()
{
    register_rest_route('zerobytecode/v1', '/generate-image/(?P<id>\d+)', [
        'methods'             => 'POST',
        'callback'            => 'zerobytecode_handle_generate_image',
        'permission_callback' => 'zerobytecode_check_permissions',
        'args'                => [
            'id' => [
                'required'          => true,
                'validate_callback' => function ($param, $request, $key) {
                    return is_numeric($param);
                }
            ],
        ],
    ]);
}
add_action('rest_api_init', 'zerobytecode_register_rest_route');

function zerobytecode_check_permissions(WP_REST_Request $request)
{
    return current_user_can('edit_post', $request['id']);
}
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Handling the Image Generation Request

This function processes the image generation request and handles communication with the OpenAI API.

function zerobytecode_handle_generate_image(WP_REST_Request $request)
{
    $post_id = $request['id'];
    $post_data = get_post($post_id);
    $excerpt = !empty($post_data->post_excerpt) ? $post_data->post_excerpt : wp_trim_words($post_data->post_content, 100);
    $api_key = get_option('zerobytecode_openai_api_key');
    $content_template = get_option('zerobytecode_content_template');

    if (empty($api_key)) {
        return new WP_Error('missing_api_key', __('Missing OpenAI API key.', 'zerobytecode'));
    }

    $prompt_response = wp_remote_post(
        'https://api.openai.com/v1/chat/completions',
        [
            'headers' => [
                'Content-Type' => 'application/json',
                'Authorization' => 'Bearer ' . $api_key,
            ],
            'body' => json_encode([
                'model' => 'gpt-3.5-t

urbo',
                'messages' => [
                    [
                        'role' => 'system',
                        'content' => sanitize_textarea_field($content_template),
                    ],
                    [
                        'role' => 'user',
                        'content' => sanitize_text_field($excerpt),
                    ],
                ],
            ]),
            'timeout' => 60,
        ]
    );

    if (is_wp_error($prompt_response) || wp_remote_retrieve_response_code($prompt_response) !== 200) {
        return new WP_Error('api_error', __('Error communicating with OpenAI API.', 'zerobytecode'));
    }

    $prompt_data = json_decode(wp_remote_retrieve_body($prompt_response), true);
    $prompt = $prompt_data['choices'][0]['message']['content'] ?? '';

    if (empty($prompt)) {
        return new WP_Error('prompt_error', __('Unable to generate image prompt.', 'zerobytecode'));
    }

    $image_response = wp_remote_post(
        'https://api.openai.com/v1/images/generations',
        [
            'headers' => [
                'Content-Type' => 'application/json',
                'Authorization' => 'Bearer ' . $api_key,
            ],
            'body' => json_encode([
                'model' => 'dall-e-3',
                'prompt' => sanitize_text_field($prompt),
                'n' => 1,
                'size' => '1792x1024',
            ]),
            'timeout' => 60,
        ]
    );

    if (is_wp_error($image_response) || wp_remote_retrieve_response_code($image_response) !== 200) {
        return new WP_Error('api_error', __('Error generating image with Dalle 3 API.', 'zerobytecode'));
    }

    $image_data = json_decode(wp_remote_retrieve_body($image_response), true);
    $image_url = $image_data['data'][0]['url'] ?? '';

    if (empty($image_url)) {
        return new WP_Error('image_error', __('Unable to get image URL.', 'zerobytecode'));
    }

    $image_id = zerobytecode_upload_image_to_media_library($image_url, $post_id);

    if (is_wp_error($image_id)) {
        return $image_id;
    }

    set_post_thumbnail($post_id, $image_id);

    return rest_ensure_response(['success' => true]);
}
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Step 7: Uploading the Generated Image

Once the image is generated, it is uploaded to the WordPress media library and set as the featured image.

function zerobytecode_upload_image_to_media_library($image_url, $post_id)
{
    require_once(ABSPATH . 'wp-admin/includes/file.php');
    require_once(ABSPATH . 'wp-admin/includes/media.php');
    require_once(ABSPATH . 'wp-admin/includes/image.php');

    add_filter('upload_mimes', 'zerobytecode_custom_upload_mimes');

    $tmp = zerobytecode_custom_download_image($image_url);

    if (is_wp_error($tmp)) {
        return $tmp;
    }

    $file_ext = pathinfo(parse_url($image_url, PHP_URL_PATH), PATHINFO_EXTENSION);
    $file_name = sanitize_file_name($post_id . '-' . time() . '.' . $file_ext);

    $file_array = [
        'name' => $file_name,
        'tmp_name' => $tmp,
    ];

    $id = media_handle_sideload($file_array, $post_id, __('Generated featured image', 'zerobytecode'));

    if (is_wp_error($id)) {
        @unlink($file_array['tmp_name']);
        return $id;
    }

    return $id;
}
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Custom MIME Types for Uploads

Ensure the correct MIME types are allowed for uploads.

function zerobytecode_custom_upload_mimes($mimes)
{
    $mimes['png'] = 'image/png';
    return $mimes;
}
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Step 8: Custom Image Download Function

This function downloads the generated image from the provided URL.

function zerobytecode_custom_download_image($image_url)
{
    if (!filter_var($image_url, FILTER_VALIDATE_URL)) {
        return new WP_Error('invalid_url', __('Invalid image URL.', 'zerobytecode'));
    }

    $response = wp_remote_get($image_url, [
        'timeout' => 60,
        'sslverify' => true,
    ]);

    if (is_wp_error($response)) {
        return new WP_Error('download_error', __('Error downloading image.', 'zerobytecode'));
    }

    $body = wp_remote_retrieve_body($response);

    if (empty($body)) {
        return new WP_Error('empty_body', __('Downloaded image data is empty.', 'zerobytecode'));
    }

    $file_ext = pathinfo(parse_url($image_url, PHP_URL_PATH), PATHINFO_EXTENSION);
    $file_ext = sanitize_file_name($file_ext);
    $tmp_fname = wp_tempnam($image_url);

    if (!$tmp_fname) {
        return new WP_Error('temp_file_error', __('Unable to create a temporary file.', 'zerobytecode'));
    }

    file_put_contents($tmp_fname, $body);

    return $tmp_fname;
}
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Final Thoughts: Creating Your First AI Plugin

The ZeroByteCode AI Featured Image Generator plugin provides a streamlined way to generate and set featured images for WordPress posts using AI.

By integrating with OpenAI's Dall-E 3, this plugin automatically creates images that match the content of your posts, enhancing the visual appeal and engagement of your site.

With detailed settings, REST API integration, and secure handling of uploads, this plugin is a powerful tool for any WordPress site looking to leverage AI for content enhancement.

We have written a more comprehensive, optimized and fulfilled the WordPress coding standards on how to create an AI Featured Image Generator WordPress Plugin.

More posts like this can be found on our official ZeroByteCode blog.

What plugin or code should we write about next? Comment your thoughts below 👇

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