How to Add a Thumbnail or Featured Image to a WordPress Post

Quick answer: Edit the post, open the settings sidebar, find Featured image, choose Set featured image, select or upload an image in the Media Library, and confirm. WordPress may call the same assignment a post thumbnail. Whether visitors see it, and where, depends on your theme and templates.

Set a featured image in the block editor

Open the post (or page) in the WordPress editor.
Open the settings sidebar with the gear or settings button in the upper-right corner.
In the post or page settings, locate Featured image.
Drag an image into the box, or select Set featured image.
Choose an existing Media Library item or upload a new file.
Confirm with Set featured image, then save or publish the post.

You can replace the image later by selecting the featured-image box and choosing another file, or remove it with the remove action. The settings sidebar is documented in WordPress’s Page/Post Settings sidebar guide.

Assign an image that is already in the post

If the image is already inserted in an Image block:

Select the Image block.
Open its More options menu.
Choose Set as featured image.
Save the post.

This produces the same post-level assignment as choosing an image from the Featured image panel. The difference is only where you begin.

Featured image versus an image in the post body

Action	What it does
Insert an Image block	Places an image at that point in the article content.
Set featured image	Associates one image with the post for use by the theme, archives, templates, feeds, or other integrations.

You can do both with the same file, but they are separate settings. Adding an image to the article does not automatically make it the post’s featured image.

Why the image may not appear

Assigning a featured image does not force every theme to display it. Themes commonly use the image on the home page or blog index, but a theme can omit it, place it in a different template, or use a custom crop. WordPress describes this behavior in its featured-image documentation.

Check the post preview and the blog index, not only the editor.
If the site uses a block theme, open the relevant template and look for a Post Featured Image block.
Verify that the post type supports featured images. A theme or custom post type must declare post-thumbnail support.
Review plugin settings that change archive cards, social images, or SEO metadata.

Display the assigned image in a block theme

In a block theme, a template can render the assigned image with the Post Featured Image block. Its available controls can include:

Linking the image to the post
Alignment and dimensions
Aspect ratio
Border and image styles

These controls affect presentation in the template; they do not change which image is assigned to the post. The exact controls depend on WordPress version, theme support, and the selected template.

Image sizes, crops, and quality

There is no universal featured-image pixel size. WordPress creates registered sizes such as Thumbnail, Medium, Large, and Full Size, while themes can register additional sizes and crop rules. Check Settings → Media and your theme documentation to see which sizes are generated.

A theme may proportionally scale an image or crop it to a fixed ratio. Some crop definitions also choose a crop position, such as center, top, or bottom. Therefore:

Use an image whose subject remains understandable when the theme crops the edges.
Preview the post card at the actual archive width.
Keep important faces, logos, or objects away from extreme edges.
Choose the smallest source that still looks sharp at the largest displayed size.
Use descriptive alternative text when the image conveys information; for a decorative image, use empty alt text where appropriate.

The WordPress Theme Handbook entry on featured images and post thumbnails explains registered sizes and theme support.

Classic Editor and plugin differences

This workflow describes the current block editor. The Classic Editor, managed hosting dashboards, page builders, and plugins can move or rename the control. Look for a box named Featured image, Post thumbnail, or similar in the post settings. If it is missing, confirm that the active theme and post type support featured images before changing code.

Common problems and fixes

Problem	Likely cause	Fix
Featured image panel is missing	The settings sidebar is closed, the screen option is hidden, or the post type lacks support.	Open the gear icon, inspect post settings, then check theme or custom-post-type support.
Image is assigned but absent from the homepage	The theme template does not render featured images, or a plugin changes the card layout.	Inspect the home/archive template and the Post Featured Image block; review layout plugins.
The image looks cropped badly	The theme uses a fixed aspect ratio or registered crop.	Choose a better-composed source, change the template ratio if supported, or adjust the registered image size.
Changes do not appear publicly	The post was not saved, or page/CDN/browser cache is serving an older version.	Update the post, purge the relevant cache, and reload in a private window.
Upload fails	File type, dimensions, size limits, or server permissions reject the upload.	Use a supported format, reduce file size, and check the site’s upload limit or hosting logs.
Social previews show the wrong image	Social or SEO plugins use their own open-graph image setting.	Set the social image in that plugin, or confirm it falls back to the featured image.

Checklist before publishing

The image is assigned in the post settings, not only inserted in the body.
The crop still makes sense on the blog index and on mobile.
Alternative text describes the image’s purpose.
The file is compressed and uses an appropriate format.
The post is saved, and the public page or archive has been checked.
If social sharing matters, the generated preview uses the intended image.

Or skip the browser setup

If you need a clean screenshot to use as a WordPress featured image, ScreenshotNeo returns a PNG, JPEG, WebP, or PDF from one GET request. It can capture a page or a selected element, wait for a selector or network idle, load lazy images, set a viewport or device preset, apply custom CSS, and use headers, cookies, authentication, timezone, or geolocation. See the ScreenshotNeo API documentation for the full option list.

curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webp

import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90)
open("shot.webp", "wb").write(r.content)

const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);

Cookie and consent banners, newsletter popups, and chat widgets are removed before the shot. Bot checks, blank pages, failed loads, timeouts, and cache hits are not billed, and response headers identify the page verdict and billing result. An MCP server lets AI agents use take_screenshot, get_page_info, and capture_pdf. The free plan includes 1,000 screenshots each month with no card; paid plans start at $5 for 3,000. Create a free ScreenshotNeo account.

Performance, reliability, and cost notes

Use an appropriately sized source image so WordPress does not repeatedly resize a very large upload.
For automated screenshots, wait for a meaningful selector or network idle when pages load content asynchronously.
Cache stable captures with a TTL when the source page changes infrequently.
For many posts, bulk capture supports up to 100 URLs per call; asynchronous jobs and signed webhooks can keep long batches out of request timeouts.
Use the usage API and the X-Page-Verdict and X-Billed response headers to reconcile captures and charges.

FAQ

Is a thumbnail different from a featured image?

In this WordPress context, “post thumbnail” is the older name for the post-level featured-image assignment.

Can a post have more than one featured image?

WordPress assigns one featured image per post. You can place additional images in the content or use a plugin with its own gallery or alternate-image feature.

Can I change the featured image after publishing?

Yes. Edit the post, replace or remove the image in the Featured image panel, and update the post.

Will changing the featured image change images already inside the article?

No. The featured-image assignment and Image blocks in the content are separate.

Why does WordPress generate several copies of my image?

WordPress and themes create registered sizes for different layouts. The theme chooses which copy to serve.