When editing graphics its important to know the legal aspects doing so. When editing images its important to sum up whether what you are doing is legal and in no way infringing someones copyrights. When creating a logo or a poster for instance, its important to make sure that the images used are that of the person who creates the logo or poster or, they have recieved the rights from the person whom owns the image/s which are used.
If a business uses an image without the persons whom owns it permission then they could be liable for damages to the owner and they could get sued. Even if an image which is owned by someone is edited, for instance changing the colours or even changing things around, the image is still copyrighted by the original owner.