Thats true, if you're using images you do not own the rights for from google, you are violating copyright laws if you aim to sell or publish it. The thing is, goku and all his likenesses are owned by toei animation, anything that uses his likeness as artwork model/etc is property of toei animation. It isn't quite the same as say; if you use a photo of a bear to do some artwork, since the bear isn't owned by anyone's intellectual property. It's owned by the photographer in that case.
If you want to avoid falling into legal loopholes creating artwork/graphics then you either must purchase stock, or you must edit it/reinvent it so it is unrecognisable. With the billions upon billions of images on the internet, people aren't going to start sending you to court unless you start making big money out of their work anyway.