I am using a Child Theme of Twenty Twelve on my WordPress photo blog.
Twenty Twelve supports Featured Images (aka Post Thumbnails), and generates a 624px wide image for every larger image I upload.
I don't actually use the Featured Image facility. I just insert my images directly into posts. And these images are just wasting server space.
I removed Post Thumbnails support by adding the remove_theme_support function call to my child functions.php. This removes the panel from the edit page, but the theme still generates the image on upload.
I could edit the theme's functions.php to remove the set_post_thumbnail_size function, but that defeats the point of using a Child Theme. Is there another way to stop these images being generated?