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It's a bit confusing.
It seems to me that the MIT license isn't really involved at all here. It can't apply to standalone illustrations, because MIT is a software license, and you're not open sourcing the code. What, specifically, is MIT licensed here?
For illustrations you want something like Creative Commons. Those licenses are not software-specific like MIT is.
Considering the Artwork is SVG, it seems like the SVG code of the artwork is under MIT