1. It should be bright image with clear boundaries, preferably with multiple colors. Fractal images fit good, for example.
Out of it you can get a beautiful kaleidoscope – see sample1.scope folder c:\Users\Public\Documents\ArtScope\.
If you move the sliders of sectors' height, remove the background and increase the number of sectors – you will receive a mandala.
Good examples of fractals can be found on the website Flickr - https://www.flickr.com/photos/kitty789/, https://www.flickr.com/photos/30383287@N03/, https://www.flickr.com/groups/technicolour_abstract_art_elite/, https://www.flickr.com/photos/abstractartangel77/.