How to regenerate image thumbnails in WordPress
Best option: WP-CLI
If you have WP-CLI installed on your server, you can regenerate all images by running this command:
$ wp media regenerate
The output should be something like:
Do you really want to regenerate all images? [y/n] y Found 165 images to regenerate. 1/165 Regenerated thumbnails for "passgen@2x-1" (ID 1921). 2/165 Regenerated thumbnails for "passgen@2x" (ID 1920). 3/165 Regenerated thumbnails for "safehouse@2x" (ID 1917). 4/165 Regenerated thumbnails for "safehouse-app" (ID 1916). 5/165 Regenerated thumbnails for "mus-app@2x" (ID 1912). 6/165 Regenerated thumbnails for "mus-app-3" (ID 1911). 7/165 Regenerated thumbnails for "mus-app-2" (ID 1910). 8/165 Regenerated thumbnails for "mus@2x" (ID 1909). 9/165 Regenerated thumbnails for "gsm-hand-1@2x" (ID 1904). [...]
Optionally, the regenerate function can take a few parameters:
$ wp media regenerate 123 124 125
will regenerate media only for those IDs.$ wp media regenerate --image_size=large
will regenerate only the thumbnails of “large”.