The ease with which images can be uplifted by third parties from websites leads many to a simple, cheap and easy way to furnish themselves with whatever image they want, for free.
Some time ago my attention was drawn to this site which exists to find stolen images lurking on the internet.
https://www.pixsy.comThey find your images and sue the unauthorised user for compensation.
This is probably far more effective than watermarking which can easily be cropped or masked, with no comeback, using this method you even stand to gain financially.
I have to say I haven't used the service (I take the view if anybody is stealing MY photographs they must be hard up!) but I know some photographers who do use it, one tells me he got over £2,000 in payouts last year.