When asked in a note on Deviant Art, 'hi can i have a hires of this transformers art (that was commissioned and created for a client's youtube channel) to use on my project, i'll give you credit mmkthx bye' I basicaly replied with this statement:
The commissioned artwork is the property of the client and the client alone gets the hires. I do not claim ownership of the characters or names, but I maintain the right (which client agrees to via paying my invoice) to use copies of all commissioned works in my gallery and promotional materials. Nothing in my gallery is for reuse (personal works or commissioned works) by anybody else except the person who commissioned it and myself for promotion of my business. Works commissioned by clients are strictly off limits to anybody else using them. My own personal works are more flexible and copies of works can be purchased at my discretion. If you'd like something like a piece that you see in my gallery or promotional material, I'd be happy to take a commission and create something new and unique for you to use that is not a direct rip off of a client's unique commissioned work.
Of course, the client can do with their commissioned art as they please. They are free to wallpaper it in their house, use it as toilet-paper, hang it on a wall, wear it as apparel or hand out copies to friends and family. I however out of respect for the client will not ever do this except for my own artworks.
Thanks!