I have just installed a clean Magento 2.3 store, and imported products and images.
The images are showing in the admin, and on the product, but the category/search pages are showing the Magento placeholder, rather than the thumbnail?
Might me cache are not generated for the images.
Run the following command once to generate cache again after assign the permission to media folder:
Rn command from magento root path sudo chmod -R 0777 pub/media php bin/magento catalog:images:resize php bin/magento cache:flush
I hope it will help you!
Thanks for the reply - tried this but unfortunately made no difference.
The thumbnail is showing in the backend and on the product page, just not on the category pages or search - all products just show the M2 placeholder image.
Make sure is you using correct imageId in your imageHelper for getting product thumbnail image.
P.S. all image ids described in vendor/theme-frontend-luma/etc/view.xml or in etc/view.xml of your custom theme
If my answer is useful, please Accept as Solution & give Kudos