It all depends on a combination of your browser window size and it’s width/height ratio as well as the ratio of your slide image.
If your browser is a lot wider than it’s height, then some of the image will be cut off at the bottom.
If your browser is a lot higher than it’s width – like on a mobile in portrait mode – the image will fill the height but some of each side will be cut off.
Things you could try;
create an image with ‘filler’ at the bottom which doesn’t matter too much if it is cut off