Horizon-scale images of the direct (n  = 0; in pink) and secondary (n  = 1; in blue) subimages of emitting accretion disks around spinning black holes whose projected spin axes are oriented vertically. The subimage centers (correspondingly colored points), given by the centroids of subimage contours (correspondingly colored dashed contours), are used to define the relative location (solid white lines) of the direct and secondary subimages. Left: prograde MAD GRMHD simulation with a_* = 0.94, θ_o = 17^∘, and R_high = R_low = 1. Each subimage is given by the ellipse whose Gaussian convolution best fits the brightness profile. We include an inset illustrating the parallel and transverse center shifts (S_∥ and S_⊥), the maximum diameter of the n  =  1 subimage contour (﹩{\hat{d}}_{1}﹩; marked with blue double arrow), and the critical curve (dotted yellow line). Right: geometric equatorial accretion disk model spanning radii r_s  ∈  [3r_g, 7r_g], shown for varying black hole spins (columns) and observer inclinations (rows). Each subimage contour is the projection of the disk’s average radius (r_s  =  5r_g).