Maximum measured photometric twist between 1 and 8 R_e as a function of the halo triaxiality T(8 R_e) for the TNG50 and TNG100 galaxies projected along a random LOS. FRs and SRs are shown with different symbols as in the legend. Smaller symbols are used to represent galaxies with ellipticity < 0.1, for which the errors on PA_phot are large. The color-bar indicates the median ellipticity measured between 1 and 8 R_e. The gray solid line shows the median of the photometric twist distribution as a function of T(8 R_e); the shaded area encloses the 25th and 75th percentiles. The amplitude of the photometric twists in TNG galaxies is only weakly dependent on the triaxiality parameter.