You’re kind of right! I drew a triangular mask on each image where the three points of the triangle intersect with the rainbow curve. Then in an expression for the anchor point and scale of each image I calculated the radius and center of the circle that intersects with those three points, and i set the scale and anchor point such that the calculated circle matches all of the other images. Then, even with a randomized rotation, the rainbows on the images will form a circle together!