I know of 2 of 3 of the links listed, never used any of them though.
1 - never heard of
2 - heard of it but never seen it used anywhere or used it myself, if I'm honest I've seen the creative commons 'copyright' more often
3 - my view on this one is more focused towards my line of work (industrial/product design) and people like inventors who come up with crazy ideas. Think of it as a 'free' patent system. I've had no need to use this even with some of my own personal work going off to larger companies without my initial knowledge (long story)
As to work that I put online, well I have a very simple view on this... if I don't want someone to 'borrow it' I don't put it online, I keep it for the client meetings etc (obviously can't show nda stuff anyway). Keeping something back also gives something to talk over in initial meetings to get a feel for a clients requirements.
You also have to be VERY careful with posting your work on sites like instagram, twitter, facebook etc but in some t&c's you give away the right for them to sell your work in various different ways etc.
In regards to client work
50% upfront (or first payment depending on length of contract) unless under a certain value where it's all requested upfront (very rare).
Work is completed under an NDA (non disclosure) on my part and I only deal with listed representatives of the client/company.
No high res imagery is sent until it's finished and 'signed off''
No editable files are sent until the end and ONLY if they were part of the contract, if not they remain my property but can only be used for the client they've been contracted for.
Final payment is requested at the end with defined payment dates - no payment by due date gets a friendly email asking for confirmation of payment because I haven't received it which normally gets it paid.
@scotty Google image search doesn't work with all sites, you can/could block your images showing in it via robots.txt