When it comes to getting things copyrighted and proving your ownerships there are many ways to go around doing this but one of the most easiest and effective way of gaining a copyright is by creating a Deviant Art Account, with this account anything you upload is automatically copyrighted to your user name which in turn is attached to your e-Mail then your personal details, and as you post it you automatically have a date stamp as it tells viewers when it was uploaded, meaning if there were any disputs about ownership Deaviant Art should be able to settle the arguement, this works very well for independant artists.
Another good thing about the copyrighting process on Deviant Art is that when uploading you can also choose license in which to release your work, such as a creative commons license allowing people to use your work for free aslong as you're credited for it's use.
One such instance of this instant copyright coming in great use was when I uploaded a short sequentially illustrated narrative, everything for this piece was created by me, first using photographs and then photoshop. During the production I did use an image from and name of a Rockband luckily the album that I used has a creative commons license allowing me to use it as long as I do not claim ownership of that said material.
If I was to get a publisher though I would first have to find out how to use the images not created by myself, most likely asking permission from the original creator. If I was denied I would have to change it, but if they request a payment I would have to organise the terms of agreement over payments before printing. If a buyer came up to me requesting to buy the rights I think I would probably sell the rights aslong as I get a share of what ever money it may bring in and get credit for it. I would probably choose this as I feel my story isn't going to go very far finacially or creatively.
Unfortunately if a client wanted exclusive rights that would be a bit tricky with my short story appearing on Deviant Art already as it has been seen by other people so it may be a case of just accepting that exclusive rights would be right out of the window. For the next time if I had something I would have to refrain from posting it on Deviant Art and getting a copyright via another medium to allow a client to purchase exclusive rights.