An image that was posted on Danbooru by its own creator.
If the image was posted directly to Danbooru without being posted anywhere else first, it will also have a non-web source.
Self-uploads are allowed on Danbooru, but be aware that Danbooru is a moderated site and uploads may be deleted if they are off-topic or aren't of sufficient quality. See help:upload and about:mod queue for details. Compare self-upload is:active versus self-upload is:deleted to get a sense of the expected quality.
