By default, WordPress does not allow HTML elements to appear in post excerpts. You may also notice, for example, that text formatting such as bold or italics also do not appear in post excerpts, for this same reason. The featured image isn’t considered a part of the post content, so it gets output at the top of the post excerpt but not included in the post itself.
There are a couple of things you can do:
- Insert both a featured image and the same image at the top of your post content. Then the featured image will appear at the top of your post excerpt and the embedded image will show up on your post page.
- Create a manual excerpt. When you are in the post editor, you should see a field labeled Excerpt below the post content field. If you do not see an Excerpt field, then click the Screen Options tab in the upper right corner and check the box labeled Excerpt. The Excerpt field should now appear. In the Excerpt field, copy the part of your post content that you want to appear in the excerpt. It can be as long as you want, and include whatever elements you’d like, including images. Now, when you update the post, you should see the image appear in the excerpt on your home page. Any text formatting should also be preserved. It’s a little more work creating the manual excerpt, but at least you have complete control over what appears in the excerpt, i.e., I hate having excerpts which end in the middle of a sentence.
