A Yourblogmaster reader recently asked for our assistance with an image problem on their website. It all started when the user switched to a new theme, which displayed thumbnails next to the post excerpt. The problem is that all the images posted after initiating the theme looked amazing, and most of the old thumbnails looked unattractive and deformed. The user attempted to change the image sizes in Settings » Media, but this did not resolve the issue. In this article, we will demonstrate how to regenerate thumbnails or create new image sizes in WordPress.
If you add an image to WordPress, it generates new sizes and saves them in the uploads folder by default. Several WordPress themes start taking advantage of this feature and create new image sizes; however, these new image sizes are only applied to images uploaded after the theme has been activated.
To resolve this issue, you must create new sizes for all previously uploaded images. This is commonly referred to as regenerating thumbnails.
Install and configure the Regenerate Thumbnails plugin to create images in newly added image sizes. After you’ve activated the plugin, navigate to Tools » Regen. Thumbnails.

When you press the regenerate thumbnail button, your theme or the Settings » Media page will begin to generate new image sizes. Depending on how many images you have on your website, it may take some time.
In Media » Library, you can also regenerate image sizes for specific images.

Your original upload is unaffected by regenerating image sizes. It makes additional copies of the images in the newly specified sizes.
It also does not remove previously saved image sizes. If you are certain that you have not used those sizes anywhere on your website, you can delete them.
We hope this article was useful in teaching you how to regenerate thumbnails and create new image sizes in WordPress.
If you liked this post, please find and follow us on Instagram, Twitter, and Facebook.