The dark matter distribution is deduced from the multiple images of very distant background galaxies that have been gravitationally lensed by the dark matter.
They are the multiple blue streaky blobs that are distributed in multiple arcs around the central set of nearby fuzzy blobs (galaxies).
Many of the blue streaks/arcs are actually multiple images of the same galaxy…
…HTH. EDIT: maybe just saying the same as above though 🙁
Paul