I don't see how anyone can '100% guarantee' that absolutely anything that is published on the internet... be it text/photo/video/artwork/-etc. Won't be stolen/copied/sold off as being somebody else's work.

You see all a person has to do is just do a 'print screen'/or, 'save image as...'/or, in the case of text: 'select All/copy/paste'. There is video downloader software which allows you to copy other people's video's, as well. I even heard that it's possible... if the image is watermarked... to use certain software... Adobe Photoshop/-etc. To get to remove the watermarked part.

So, it's certainly easy enough to be able to steal stuff that's been published online; and, then, go pass it off as being your 'own' in order to go sell.

Then, when one adds in such factors as... the people stealing it could be located absolutely anywhere in the whole wide world; and, that they don't need to tell anyone that they went and stole it from you... nor ask you for permission to 'copy/steal/borrow' it...; then, really, it becomes impossible to know who stole what/or, indeed, where on earth these people might be located; nevermind, finding them to go take them off to court; indeed, does anyone even want to go through the financial pressures -(not to mention, emotional upheavals)- of facing a court battle... nevermind, that court battle being located in another land, somewhere... where your own local law might not even apply...?

What I'm saying is... the only way to know your own material is, well and truly, 'safe' is just NOT to publish on the internet at all. Of course, you might loose money that way... by not selling anything online; but, then, you have to make a decision for yourself... do I wish to make money online/or, would I rather sell offline, instead. Of course, in the 'offline' world... people can and do still steal/forge stuff...; so,...?!