brotify, I suggest searching for Creative Commons licensed fractals on Flickr.

Start at this page. Check all the boxes in the Search by content type section. In the Creative Commons section, check Only search within Creative Commons-licensed content; check one or both of the boxes below it, if appropriate. Then click the Search button.

Please be sure to understand and abide by the terms of the particular Creative Commons licenses on the images you choose.

Good luck!

Ken