Add per-episode GelSight reference images: episode_NNN.gs_ref_{left,right}.png = the 1st-percentile-intensity frame at native 640×480 (the 'quietest' / least-contacted moment of the episode). Use these as the diff baseline in any visualization — gives a stable 'this is what's currently pressing on the gel' diff rather than 'change since the start of this clip'. 27 episodes × 2 sides = 54 files.