Is it possible for a plugin to force reading and writing of uploaded images to a database instead of to a filesystem?

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Yes, you should have quite reasonable options to customize upload, there are plenty of existing solutions around.

As for specifics I am not sure on “database” as image storage option. They typical solutions that I’ve heard of are:

  • dedicated location behind CDN (or some variation of);
  • dedicated image storage service, such as Amazon S3.