Featured image on a post
Where it appears
On a single post the featured image is printed under the subtitle and above the post content, at the full width of the content column.
It is never cropped on a single post — the thumbnail ratio setting applies to the listing only. The image keeps its own proportions.
Turning it off
Customize → Single post → Display thumbnail on single post? On by default.
Turn it off when your featured images exist only to fill the listing cards and would be redundant at the top of the post itself — which is a real and reasonable arrangement. The listing keeps its thumbnails; it has its own switch.
Captions
If the image in the media library has a caption, it is printed under the featured image on the post.
This is worth using: a photo credit, a location, a date. Set it on the attachment (Media → the image → Caption), not in the post. Basic HTML is allowed, so a link back to the source works:
Photo by <a href="https://example.com">Someone</a>
What size to upload
Around 1400px wide is right. The theme registers 1400 × 9999 as the featured
image size, so anything wider is resized down to that and anything narrower is
left alone.
WordPress generates the smaller variants automatically, and the theme tells the browser which one to use for the box the image is actually being drawn in — so a grid card downloads a card-sized file, not a full-width one. Nothing to configure.
Do not upload 4000px camera originals. They cost your visitors bandwidth for pixels no screen will show.
Alt text
Set it. Media → the image → Alternative Text, or in the featured-image panel of the editor. It is what a screen reader announces and what search engines read.
Describe what is in the picture, not the post: “A market stall stacked with peppers”, not “Lisbon food guide featured image”.
If the image is purely decorative — a texture, a divider — an empty alt is the correct answer, and better than a description nobody needs.
Password-protected posts
The featured image is not printed on a post that requires a password, in the listing or on the post itself, until the password is entered.
Related
- Listing thumbnails — crop, border, radius
- Wide and full width blocks — for images inside the post