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To require a featured image, solve two separate problems: first enable the Featured Image control, then add a publication-time validation rule. Declaring post-thumbnails support only makes the control available; it does not stop an editor from publishing without an image.
1. Make the Featured Image control appear
WordPress calls a featured image a “post thumbnail.” It is the image associated with an individual post, page, or custom post type and can be displayed in archives, headers, or the single-post layout. The active theme must declare support before the control appears on the edit screen. WordPress’s Theme Handbook states that themes must declare support for the interface.
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Enable support in the theme
Add this declaration in the active theme’s functions.php file or on the after_setup_theme hook:
add_theme_support( 'post-thumbnails' );The declaration must run before WordPress reaches init. The add_theme_support() reference documents the timing requirement and supported feature registration.
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Limit support to standard posts when appropriate
If pages or other content types should not have featured images, pass the permitted post types as the second argument:
add_theme_support( 'post-thumbnails', array( 'post' ) );That scope controls where the editor interface is available; it is not an enforcement rule.
Check a custom post type
A custom post type must support thumbnails as well. Inspect its register_post_type() configuration and ensure thumbnail is included in the post type’s supports array, or add support through the post-type support API. Use post_type_supports() to verify whether a type currently supports the feature.
If support is correctly registered but the panel is still absent, check that you are editing the intended post type and that the editor has not hidden the panel in its preferences or screen settings. Those visibility settings are separate from theme support.
2. Understand why support does not make images mandatory
The support declaration answers “May this content type have a featured image?” It does not answer “May this post be published without one?” WordPress can therefore show the panel while still allowing a post to move to Published, Scheduled, or another status with no thumbnail.
A mandatory-image policy needs a second layer that examines the post at the point where publication is requested and blocks that transition when no featured image is assigned. Decide which statuses and post types the policy covers before implementing it—for example, you might require an image for public posts but not for drafts or internal notes.
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3. Choose an enforcement route
| Route | What it can enforce | Questions to verify |
|---|---|---|
| Editor plugin | Can add an editor-side check and prevent publication when the image is missing. | Does it support the block editor and classic editor you use? Does it block publication or merely display a warning? Is it maintained and compatible with your WordPress version? Does it cover scheduled posts and every required post type? |
| Custom server-side validation | Can enforce the rule centrally during the relevant publication transition, including workflows that do not use the visual editor. | Is validation limited to the intended post types and statuses? What response does an editor receive when the check fails? Have current WordPress hooks and status-transition behavior been verified on your version? |
| API or workflow validation | Can reject automation requests before a post is published, provided the workflow checks the image requirement. | Does every client perform the check? Is the attachment valid and available to the site? Are retries, scheduling, and updates handled consistently? |
A project named Require Featured Image describes an editor-side publishing block. Treat it as an implementation to evaluate, not as a current compatibility recommendation: verify its WordPress.org listing (if any), update history, supported editors, and status handling before relying on it.
4. If you build the rule yourself
Keep the validation requirement explicit rather than tying it only to a particular button in the editor. A robust workflow should:
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- Identify the post types covered by the policy.
- Run when a post is being moved to a public or otherwise prohibited status.
- Check whether a featured-image attachment is assigned.
- Reject or prevent the transition when the assignment is absent.
- Return an actionable error so the author knows to select an image and try again.
- Permit drafts or exempt content types when your editorial policy allows them.
WordPress’s exact hooks, editor requests, and status transitions can vary by version and workflow. Verify the current developer documentation and test the rule in a staging site before deploying it; do not assume an editor-only check protects imports, scheduled jobs, or REST clients.
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5. Enforce the requirement for REST API publishing
For REST API requests, WordPress identifies the featured image with the attachment ID in the featured_media field. A request can therefore include, for example:
{
"title": "Example post",
"status": "publish",
"featured_media": 123
}The ID must refer to a valid media attachment. The Posts REST API reference documents the field, and the posts controller’s featured-media handler documents how WordPress processes it, including clearing the thumbnail when an empty value is supplied.
Supplying featured_media is field handling, not a site-wide policy. If publication must be blocked when the field is missing, the API workflow must validate that condition before—or as part of—the publish operation. Apply the same rule to every integration that can create or update posts; otherwise an importer may bypass the editor safeguard.
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- Create a draft of each covered post type with no featured image and confirm that saving a draft still behaves as intended.
- Attempt to publish it in every editor your site supports and verify that publication is blocked with a useful message.
- Select a valid image, publish again, and confirm the post reaches the intended status.
- Test scheduled publication, if used, because a check that works only when clicking Publish may not cover the later status change.
- Send an API request without
featured_media, with an invalid attachment ID, and with a valid ID. Confirm the workflow rejects only the cases your policy forbids. - Test exempt post types and existing posts so the new rule does not unexpectedly alter older content or internal workflows.
Common failure modes
- The panel is missing: confirm the active theme declares
post-thumbnails, the declaration runs beforeinit, and the post type supportsthumbnail. - The panel appears but publishing still succeeds: theme support is working; an enforcement layer has not been added or does not cover that editor/status.
- API posts publish without images: the client is sending no ID, or its workflow has no required-field validation. Add and test a policy check rather than relying on the REST field alone.
- A plugin blocks one workflow but not another: compare its coverage of block editor, classic editor, scheduled publishing, custom post types, and API-created posts, then supplement or replace it with server-side validation where necessary.
Recommended setup
Enable and scope thumbnail support in the theme and custom post type first. Then enforce the requirement in the layer that matches how your site publishes: a maintained plugin for a simple editor-only workflow, server-side validation for a central rule, and explicit API validation for automation. Test each publication path and status you actually use; only then can “featured image required” be a reliable site policy rather than a visible but optional field.
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