Rangoli artists often share elements -- for example, lotus flowers and leaves, swans and parrots, and certain human imagery. Many times these elements are copied and re-arranged and other times, an artist may create unique elements by hand, without copying. When elements are original, the copyright can be claimed by the artist. When elements are in the public domain -- taken from much older works -- a derivative copyright can be claimed as to the manner in which the elements are re-arranged and as to new elements that are added. But the less modification that is made to public domain elements, the thinner (and less enforceable) the copyright. In other words, the degree of originality matters when seeking to enforce rights over a traditional Rangoli work.
If you copy. If you reproduce someone's original work, or derivative designs over which people claim copyright, then the owner may pursue you in court. That's provided that the owner can register the work, convince a court that it is protectible, and that your use does not constitute fair use. That may be an uphill battle for some Rangoli creators, and not so difficult for some others.
Inadvertent duplication. As for Question #2, if you inadvertently duplicate a Rangoli work -- that is, you create it independently without copying -- then you would not be liable for copyright infringement. As long as you can prove you didn't copy and you created something independently, there is no infringement.
Bottom line. We think there are so many centuries of Rangoli art available, and so you should be able to safely include older public domain Ragnoli works. If you want to reproduce a work and you're unsure of whether it's protected, our suggestion is to keep the image as small as possible as the trend lately has been to permit thumbnail usage of artwork as a fair use. Finally, avoid copying and reproducing large groups of Rangoli from websites. That's because some Rangoli collections may qualify as a compilation copyright which protects the choice and order of the collection but not the individual works.