Ok there's seem to be a lot of confusion regarding the supposed trackers on images. Let me make this clear, there is no such thing. because that's a malware, and modern firewall and antivirus are very decent at catching these stuff (yes even Windows Defender).
However, there are indeed ways that creators can catch the original buyers for sharing. There are a few methods to do this like:
_putting metadata into the pictures saying who's buying it
_putting an "invisible layer" into the pictures that say who's buying it
_etc.
All of these methods require the creator to generate a UNIQUE URL for you to download the sets. Which means they need to have their own server to automate these stuff as they have hundreds, even thousands of buyers. Byoru is not one of them as she sells via Fantia and Patreon, these services don't do any of that.
As far as I'm aware, only Kokuhui(?) is able to do this for a few times, and even then her sets still get leaked regularly.