Thank you for your post.
When an image is put into a Container field where the formatting is set for (default) "Reduce image to fit", a thumbnail is temporarily created. If you then go into Manage Containers, and click on the Thumbnail tab, you will see the option "Generate and store thumbnails of images" checked with the sub-option "Temporary storage". If you want the image to be stored permanently in the file (making for faster display), then change the sub-option to Permanent storage. For those images that are either embedded or stored using secure storage, the thumbnails are also encrypted in permanent thumbnail storage. When you change from temporary storage to permanent storage, it may take some time to update the file, especially with 7000 images.
If you have a calculation using GetThumbnail function, this will create a separate image.
I don't have experience with SuperContainer, so you may want to contact 360Works for guidance about possible interference.