Animation clips are protected by copyright laws just like photographs, written works, music, and other art forms. Animation clips and clip art are just other forms of art and all the same copyright laws apply. Just because something is published on the web or can be easily copied does not mean it can or should be copied. Animation clips belong to the creator and you need permission from the owner to use it for any purpose. If you are the owner of the art work and discover illegal use of animation clips then you have legal recourse. You can ask the person using your material to cease and desist or you can pursue the matter in a court of law.