I completely disagree with the original proposal.

First, it's not possible to control whether all due credit was given in any particular image, as some have already noted. If it can't be controlled, then it can't be made into a rule. It's as simple as that.

Second, why credit only content creators? What about the tools? The tools are as important (if not more) to achieve a certain result. If I'm a traditional painter, I should credit the brand of paint, brush and canvas I used. If I'm a digital artist, I should credit the monitor brand (vital to get a decent color adjustment), plus all the software I used in my workflow to produce the image (and most artists use a lot of tools), plus all the fonts that I used to title the image, plus the inspiration sources, etc, etc, etc.
What about your training and education? Shouldn't you credit your art teacher? He made 90% of what you are as an artist! Everything contributes to that final image!

So, either credit all or nothing. To stay halfway is to say that some are more important than others and that is not fair.