Many Syngency websites use a classic "book" slider for their talent portfolios. This lets visitors quickly "flip" through the gallery:
For this layout to work correctly, portrait images need to be "paired" together, with any landscape images positioned between the pairs of portrait images. This is simply because a single portrait and a single landscape can't both fit on a single page of the slider.
The gallery below is correctly ordered, with 6 portrait images in 3 pairs, a single landscape image, and then the remaining portrait images.
If the landscape image is moved in between the third pair of portrait images, the layout of the slider won't work – so it's important to keep the order correct.