When my daughter brought home last year's yearbook this fall, I was surprised to find 40+ sports pictures, snagged directly from my Zenfolio website, with my watermark on them had made the grade....without my permission. I know everyone on here says it's a no-no to give your pics away, but I would have gladly let the yearbook kids use them had they just asked. I went to the principal and she was dumbfounded and disgusted. My daughter got a free yearbook and I was asked to come talk to this year's class about copyright and photography. I also received a forced apology letter from the previous teacher who had allowed this to happen. She still gives me dirty looks when she sees me!
First you should send a letter of inquiry, at this point you have no idea how your images have been used. Have they been used in print? Are there web sites you don't know about? How can you invoice without knowing the extent of the damages done to you? Reading your post again perhaps you should at least consult a lawyer. Would you hire a lawyer to take your wedding photos? I think not, being a photographer you are not the best person to handle legal issues.
I let my school use my photos for free because there is something to gain for all by doing so; the school has quality imagery, and I am fostering goodwill and ensuring I am less dispensable. That reminds me; I must remember to draft some bilingual model releases...
TWIP often has information about copyright and the need to register your images. Registering must be done within 90 days of capture and you can create a ZIP file of however many images you'd like to register (from the previous 90 days shooting) and send them off with payment.
