a fairly easy way would be to apply the blend effect to the ‘front’ image. use the ‘blend with layer’ property to select the ‘back’ image (that image needs to be in the comp, but does not need to be active — click the ‘eyeball’ icon to hide it; nor does it need any animation).
now you could animate the ‘blend’ property with hold keyframes to change between front and back images as needed (toggle between 100 and 0), or you could add an expression to the property (select the property in the timeline, then choose animation>add expression) and paste this expression into the expression field:
if (toCompVec([0, 0, 1])[2] > 0 ) value else 0
if you want to know more about this expression, i copied it from dan ebbert’s site here:
https://motionscript.com/design-guide/invisible-facing-away.html
he had written the expression to go into the opacity properties of two layers, but the blend effect makes it only necessary for the ‘blend’ property, plus the ‘back’ layer won’t need to be animated or parented and flipped.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW