The following KB articles relate to this topic:
Photo carousels can be used as a sort of gallery to display multiple images or as an advertising tool (by creating image banners). The size of your photo carousel depends on the dimensions of your images. Resize your images to resize your photo carousel.
The photo carousel content block offers the ability to replace large images with smaller versions for display on devices. This is a recommended practice when building responsive websites due to the long time it takes to load large images on tablets and mobile devices.
Below is an example of a photo carousel that has been used to display large images.