On another note, how on earth did you discover what they had done?
Alain, I was wondering the same. Coincidence?
I can only talk of experience in a European context. I had a state agency steal many of my work and use it for their website. I spare you an epic description how it came to that.
I contacted them in a friendly way, and the funny thing was, next day half of the pictures disappeared, by far not all of them however, and a annual brochure was still full with my pictures.
Now, I do not believe in justice other than that a bunch of blood sucking solicitors and barristers will make sure they get an insane cut for any breath they take on your behalf, so I decided against legal action, but wrote another letter myself.
Here I quoted law text and possible implications, the full whack everything I could find in context. To this letter I attached an invoice for usage of my work. I made a reasonable invoice based on licensing for web use. However, it ended up being somewhat a total of Euro 2,500 all together. There were no penalties or anything else just reasonable pricing.
I set a short 10 days ultimatum for payment, otherwise the matter would be out of my hand and court activities would be inevitable. Of course, no payment came through, the Irish State is bankrupt!
So 11 days later I called the payroll department and increased the pressure.
The following day all my pictures disappeared.
Now, I have to say, I did not expect justice at all, my goal was to get them !@&^@£ to take down my work from their site. By sending an invoice and threatening legal actions, and.... helluva lot of publicity.... I got them to take all from their site.
Needless to say, very distressing experience, and time consuming to deal with.
It is a good idea to immediately send an invoice when you see your work being stolen, make this a matter of records.