EXPERIENTIAL : AUTOMOTIVE
Slideshow demonstrating how smaller images are stretched to fill, which looks bad (this behavior cannot be changed):





Slideshow demonstrating how extra-wide images will shorten the height of the entire gallery (here the culprits are the Nissan Booth images):


















SOLUTION:
Select an ideal image dimension (height and width) for the slideshow container, and only upload high res images that can fill this size without stretching.
For odd-shaped images, e.g. Nissan Booth images,, re-create them on a canvas in Photoshop with white space above and below to match the dimensions of the other images.
Find high resolution source files, so images look good.