In 2014 I did a sample audit of 6 random images out of the 500 I had online here.
For each of those 6 images I found illicit uses outnumbered authorised use 12:1
By authorised I don't mean paid for. I mean people who'd had the decency to ask.
Of the unauthorised, almost none credited me as the source, and most asserted someone else's copyright. Virtually all had the metadata removed, a criminal offence.
If that sample is typical, 500 images represent 6,000 infringements. Very few of which could sensibly be pursued. The most that I could do is issue take-down notices for the most objectionable ones. Many weeks of unpaid work.
I refuse to spend the rest of my life blocking would-be hackers and playing Whack-A-Mole with copyright infringements. As everybody says "if you don't want it stolen, don't put it on the web". So now I don't.