Hi D.,
We have cut the image size into three sizes.
add_image_size( 'magcast-slider-image', 666, 810, true ); // for slider
add_image_size( 'magcast-large-thumb', 965, 575, true );
add_image_size( 'magcast-small-thumb', 467, 350, true );
So use better a big size image then it will automatically cut into pieces and will be displayed as in our demo site. If you have already uploaded the image then one regenerate thumbnails using regenerate thumbnails plugin.
Thank you