Triple buffering never drops images on the input side. But if the processing can’t keep up with the rate of images coming in then you’ll miss frames. However, you’ll never have to deal with old frames.
Image fifo mode makes sure you capture all frames, even old frames.
The difference becomes apparent when you have an image fifo of like 100 images and you add a delay between reading frames. You will get a slow-mo like effect with image fifo mode then.