Complex sentence: Shepard Fairey, the artist behind the poster, sued the Associated Press seeking to establish that his Hope poster did not infringe the AP's copyright of a shot taken by AP freelancer Mannnie Garcia.
Split into simpler sentences: Shepard Fairey, the artist behind the poster, sued the Associated Press. He sought to establish that his Hope poster did not infringe the AP's copyright of a shot taken by AP freelancer Mannnie Garcia.