It really is very easy if we simply decide what we can cut out and still keep the essential theme! In the above copyright-free image we might decide to cut out the ballerina and the man in the background on the right, get rid of the figures on the left and turn the striped cloak on the left into a tree trunk.
The wide-cut image of the dancer looking into her mirror could be set beside a wild and fanciful tree on the left and perhaps an added curtain or simple backdrop on the right would add to the theme of the Theatre! Enlarged to a rug pattern size, the lines of the dancer are easy and flowing without too much detail. Also using wild colours would help the overall celebration of a theatrical production!
I love the Dover books with the permission-free images and images from antique rugs and decorations! When I use or adapt them, I know that I am not infringing on anyone's copyright and we can all use these images to design from!