As a tagger in a group, I know I can't put other people's names on copyrighted material, such as Disney images or Garfield images. How is it that a popular site on the internet, PicGifs offers the above free? That's confusing. If you download a picture of garfield from the site is that legal??

What's a tagger and what sort of group are you in?

You can't alter a copyrighted images so as to falsely represent that you created them. Is that what you mean?