It is relatively easy to register new image sizes in your WordPress theme. After you have told your system how big your images should be, named them and decided how to crop them, you are free to distribute images anywhere you want. But what about the old images?
If you have used one of the techniques we have showed you, you have prepared the turf for new images. Whether you use newly register image sizes for post thumbnails or allow authors to use them in posts, new rules apply only for those images which are uploaded after you’ve made the change in the functions.php file. To change the older images, we suggest using Regenerate Thumbnails plugin.
- Go to Plugins->Add New
- Search for “Regenerate Thumbnails”
- Install and activate the plugin
- Navigate to Tools->Regen.Thumbnails
If you want to resize all of your images, simply click on the “Regenerate All Thumbnails” button and wait for plugin to do the hard work.
If you want to see the images which are going to be resized, or if you want to resize only some of the images, go to your Media Library where you will find a new option under “Bulk Actions” and one beside each picture in the gallery.
The good thing about the plugin is that it doesn’t delete your original images. It will only create new image sizes which you can use in your theme, while the original ones will be left for you to use them later or delete manually if you decide you don’t need them.
That’s it. Enjoy your new thumbnails or check out Simple Image Sizes plugin which can do the same thing.