These are public images. From Midjourney's license terms

Please note: Midjourney is an open community which allows others to use and remix your images and prompts whenever they are posted in a public setting. By default, your images are publically viewable and remixable. As described above, you grant Midjourney a license to allow this. If you purchase a private plan, you may bypass some of these public sharing defaults.

Read more here: https://midjourney.gitbook.io/docs/billing#commercial-terms