If you are migrating from another theme that supports WordPress featured images functionality, you will notice that all your images that were uploaded after activating the theme are looking just as expected but your old images might appear stretched or pixilated.
Trying to adjust the size manually from the Settings will not correct the problem. All your image thumbnails must be regenerated in newly defined dimensions that your current theme supports.
Fortunately, this process is a lot easier with a plugin called Regenerate Thumbnails that will automate the whole process:
- Install the Regenerate Thumbnails plugin and activate it.
- After activating the plugin, navigate to Tools.
- Click Regenerate Thumbnails.
- Now click Regenerate Thumbnails For All X Attachments and wait until all thumbnails are completely regenerated.
- That’s it! now check your website again and all your featured images should appear in the correct size.